to those hit hard by the pandemic. the post-holiday travel nightmare. tonight, chaos at airports across the country. thousands of flights cancelled just since christmas eve. passengers left scrambling, now racing to get home. major airlines blaming covid-fueled staffing shortages and poor weather conditions. tonight, that dangerous winter blast. the powerful system slamming the west. in washington, cars getting stuck in whiteout conditions. feet of snow shutting down highways like i-80 in california. tonight, as millions take to the roads for their return home, when is the best time to travel? remembering a legend. archbishop desmond tutu, the nobel prize winner who helped bring an end to apartheid in south africa. the tributes coming in tonight. a deadly christmas day house fire killing a father and two children. authorities point to the lights on their tree as the likely cause. tonight, how to keep your home safe this holiday season. it's also gift return season. how to send back those unwanted presents. you won't believe how many returns are expected. and america strong. celebrating holiday heroes. people skipping their own celebrations to give back to those in need. >> announcer: from abc news world headquarters in new york, this is "world news tonight." good evening, everyone. thanks so much for joining us on this sunday after christmas. i'm linsey davis. we do begin tonight with the pandemic. as omicron rapidly spreads throughout the nation, millions of americans now heading home returning from gatherings with family and friends this holiday. today dr. fauci calling the variant extraordinarily contagious, saying that he expects the number of cases to go much higher. a sign of the times, perhaps the image of this holiday season. long lines, people waiting to get tested or to get home kits. in many places, both are in short supply. though some preliminary studies show omicron appears less severe than other variants, health experts are urging people to get their shots, saying they are most concerned about the millions of unvaccinated americans. officials are also seeing a rise in pediatric infections. abc's phil lipoff leads us off tonight from new york. >> reporter: tonight, health experts warning of an omicron surge on top of a surge after millions finished gathering and celebrating christmas with family and friends. dr. anthony fauci urging americans not to get complacent despite several studies suggesting this new variant might be less severe than delta. >> every day it goes up and up, and it likely will go much higher. >> reporter: outside minneapolis, the janovsky family gathering for the first time in two years for christmas. >> this year is definitely a lot different because we all feel safer because we were all able to get vaccinated and boosted. >> reporter: but for so many americans this holiday, getting tested has not been easy. at this test distribution site in brooklyn, pushing and shoving led to police being called to manage the crowd. in manhattan, now 1 in 60 people have tested positive for covid just this week. north of the city, this woman arriving an hour early to get an at-home test. but the site running out of them 47 minutes after opening. today dr. fauci acknowledging that president biden's promise to distribute 500 million free at-home rapid tests is a good one but needed to happen sooner. >> we've obviously got to do better. i mean i think things will improve greatly as we get into january, but that doesn't help us today and tomorrow. >> reporter: dr. ashish jha telling our jon karl the best way to protect yourself is to get vaccinated and boosted. >> are we going to need to be getting kind of an infinite number of boosters here? >> i think we don't know at this point. is it possible we'll need more boosters? possible. maybe even likely. when i think about it, i get an annual vaccine for the flu. i guess i get an annual booster. >> reporter: tonight, an alarming increase in pediatric hospitalizations in new york and in other parts of the country. ohio, texas, pennsylvania hit particularly hard. >> only a third of children under 18 are fully vaccinated at this point, and while we know, you know, covid is less severe in our kids, we also know that it's had a real impact in our kids across severe illness and death. >> reporter: 170,000 children testing positive for covid last week alone, an increase of nearly 28% in just two weeks. and it's the unvaccinated, health experts say, are still most at risk. in ohio, 18-year-old sarah golembiewski lost both of her parents and her aunt to covid just days apart and a few weeks before christmas. all of them had turned down the shot. >> if my parents got it, it would have saved their lives. once they're gone, they're gone, and there's nothing you can really do to get them back. >> reporter: president biden and the first lady acknowledging this christmas is a difficult one, telling americans they are praying for those who have lost loved ones during this pandemic and for whom this christmas falls on heavy hearts. we pray for you to find strength from sorrow and purpose from pain. >> the president as consoler in chief once again there. phil lipoff joins us live from new york city. tell us about this first of its kind vaccine mandate set to go in effect in new york in just a matter of hours. >> reporter: linsey, that mandate you're talking about is for private sector workers. it will begin tomorrow and will affect roughly 184,000 businesses. if an employee only has one shot by tomorrow, they'll just have to show proof of when they plan to get that second dose. linsey? >> phil, thank you. and on this, one of the busiest days for people flying home, omicron is contributing to thousands of flight cancellations this holiday creating a travel nightmare for some, and a dangerous winter blast in the west is only making matters worse, impacting flights and the millions taking to the roads. here's abc's janai norman. >> reporter: tonight at airports around the country, thousands of travelers are scrambling to rebook flights as that wave of covid-linked cancellations continues. >> i'll probably just end up getting a hotel and then try in the morning. >> reporter: nearly 1,000 canceled christmas day. more than 300 just on delta. united and jetblue, not far behind. and over 1,000 cancellations again today. >> we left the house at 7:00 friday morning, and we just got back here half an hour ago. >> and you have yet to actually be on vacation? >> true, true. but we did sleep in a hotel room. >> reporter: airlines blaming the rising number of coronavirus cases forcing staff and crew to quarantine or call in sick. another major factor, a powerful storm system slamming the west. whiteout conditions in washington. cars sliding and buses stuck in seattle and unbelievable snow shutting down a 70-mile stretch of interstate 80 from colfax, california, to the nevada state line. our matt gutman in truckee. >> check out that stop sign, almost completely submerged. that pile behind it almost 15 feet high. and underneath the white here is actually blacktop covered with hard-packed ice. that's why so many hundreds of people who have crossed this area have been stranded here for days now. >> reporter: nevada highway patrol responding to a 20-car pileup with injuries reported. treacherous driving with more than 100 million traveling by car this holiday. linsey, tomorrow in the new york area, congestion levels are expected to be up over 350% from 4:30 to 6:30 p.m., so that evening commute time. in the d.c. area, traffic levels expected to be up over 250% in the late morning, from 9:30 a.m. to 11:30 a.m. the busiest time to fly home, next sunday, january 2nd. so plan accordingly. linsey? >> some helpful travel tips there. thank you. blinding snow is making some trouble on the roads. let's get straight to meteorologist danielle breezy from our affiliate wkrn in nashville about what travelers can expect next. hi, danielle. >> hi, linsey. well, we have dangerous winter weather impacting millions of americans across the western third of the country. take a look at all these alerts you can see here from california to the great lakes. more heavy snow, strong winds, and that avalanche danger from the sierras to colorado. bitter cold air across several states with windchills that will be in the teens tomorrow morning in seattle, dipping well below zero in parts of montana. to the east, another day of above average temperatures in chicago through new york with unusual december warmth in the south. highs will be in the upper 70s in austin and tupelo, and that will challenge records on monday. we're also going to challenge records right here in nashville as we are on par to be one of the warmest decembers on record. linsey. >> that warm streak continues for much of the country, danielle. thank you. tributes are pouring in from all over the world remembering archbishop desmond tutu. if nelson mandela was the heart of the anti-apartheid crusade, tutu was its soul. he died today in south africa at 90. when asked how he wanted to be remembered, tutu once said he loved, he laughed, he cried, he was forgiven. he forgave. here's abc's james longman. >> reporter: his was a laugh and joy that inspired millions. but underneath that smile, desmond tutu had a steely resolve to fight injustice. >> our march to freedom is unstoppable! >> reporter: alongside nelson mandela he fought to end apartheid in south africa and he became an iconic spiritual leader and global peace advocate. >> to be members of one family. ♪ >> reporter: his charm allowing him to champion serious issues which in later years including gay rights and the environment. and tonight tributes are pouring in from around the world. barack obama awarded him the presidential medal of freedom in 2009. >> desmond tutu possesses that sense of generosity, that spirit of unity, that essence of humanity that south africans know simply as ubuntu. >> reporter: he today called tutu a friend, a moral compass for me and so many others. president biden sending his condolences to tutu's wife leah and their family saying his legacy transcends borders and will echo throughout the ages. queen elizabeth praising him as someone who tirelessly championed human rights in south africa and across the world. and south africa's president heralding tutu as a hero from a generation of outstanding south africans who have bequeathed us a liberated south africa. tutu became the first black archbishop of cape town, but his childhood was spent under white south africa's brutally enforced apartheid system. he campaigned for economic sanctions and in 1985 when the uk and u.s. were eventually convinced to pull all investments from the country, it crippled the economy, forcing the apartheid regime to reform. he had been awarded the nobel peace prize a year earlier which he credited with helping signal the beginning of the end of apartheid. free elections were held in 1994 and at 63 years old, tutu cast his first vote. >> the hearing of the truth and reconciliation commission is now in session. >> reporter: he chaired the truth and reconciliation commission to investigate crimes during white minority rule and later became a critic of a south african government he thought hadn't delivered on his dream. >> we dreamt about a society that would be compassionate, a society that really made people feel they mattered. >> reporter: he'll be remembered for his wit and wisdom, a man who used humor to inspire hope. >> there's a lot of awfulness in the world. >> yes, i know. >> and most of us know that. but what we don't also recognize is there's a great deal of good. >> reporter: desmond tutu was described as the conscience of his nation. his struggles for universal human rights and racial equality is an example that has shone through the ages, a lesson as relevant today as it ever was. linsey. >> known as the voice of justice. james, thank you. to myanmar now. the u.s. embassy is condemning an attack that it says left at least 35 people dead. save the children reports two of its staffers are now missing. there are reports that soldiers forced people from their cars, arrested some, and killed others, later burning their bodies. the military government is not commenting on the reports. now the christmas day tragedy in quakertown, pennsylvania. a house fire claiming lives of three family members, a father and two young sons. firefighters encountering intense flames. the mother and oldest son managed to escape. officials are investigating whether the family's christmas tree was to blame. here's abc's zachary kiesch. >> reporter: tonight there are three dead and two others bearing an unimaginable loss. >> we have three people that are unaccounted for. >> reporter: after a christmas morning fire burned down this quakertown, pennsylvania, home, killing a father and two of his sons. eric king and his sons liam, age 11, and patrick, 8, seen here in a family photo posted on the crowdfunding platform gofundme, died in the blaze. eric's wife kristen and their oldest son, brady, escaped and were treated for injuries at a nearby hospital. >> i couldn't see anybody, so i thought they got everyone out. bt, you know, it was kind of sad -- it was really sad to realize that in the end, not everybody was saved. >> reporter: investigators now suspect that a dried out christmas tree may have been to blame. >> we're looking at the christmas tree that may have ignited as a result of christmas lights on that christmas tree. >> reporter: in a recent study, the u.s. consumer product and safety commission estimated that between 2013 and 2015, there are about 100 christmas tree fires each year, resulting in 10 deaths and costing $12 million in property damage. thousands have rallied behind the surviving family members. an online campaign raising more than a half a million dollars in a little more than 24 hours. >> he was in my class. he survived. his mother survived. i knew them, and then i got the news that sadly his father and his brothers died. >> reporter: experts say this tragedy really underscores the importance of safety over the holidays. that means making sure your tree is watered and also checking those smoke detectors. linsey. >> a warning for all of us there. zachary, thank you. next, we turn to a holiday tradition, the day after christmas returns. the rush is on for many to exchange those unwanted gifts. here's abc's zohreen shah on some ways to avoid the hassle. >> reporter: with all the presents unwrapped, many americans are now asking themselves, can i return this? experts estimate there will be $120 billion worth of returns this holiday season. every retailer has its own set of rules on returns based on the date of purchase. but the good news is for a second year in a row, retailers are being extra generous with their policies. many like amazon and target allowing gifts purchased as early as october to be returned until the end of january. >> in a lot of cases, you can return gifts that were purchased online in-store to a retailer's in-store location. >> reporter: some of the same old rules of returns still apply. might ha tsettle fortore is not it. pro t hld on to those gift cards. even if you don't want it, you can potentially sell it online for much of its original value. experts say many of the things we return end up in landfills so if you don't want to return, regift, resell, or just donate to charity. linsey. >> some helpful tips there. thank you, zhoreen. happy holidays to you. there is much more ahead on "world news tonight" this sunday. new images tonight of that missing 3-year-old girl in san antonio. and covid is now breaking out on land and at sea. ♪ we all need a rock we can rely on. to be strong. to overcome anything. ♪ to be...unstoppable. that's why millions rely on the strength and financial guidance of prudential to achieve 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"spider-man: no way home" raking in more than $1 billion globally. it's the first blockbuster of the pandemic to make that much at the box office. marvel is a division of disney, abc's parent company. and when we come back, people skipping their own holiday celebrations in service of others. ♪ some things can't be tried at home. where next? with capital one, the possibilities are unlimited. introducing venture x, our new class of travel card. 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