researchers noticed an activation in the part of the brain that coordinate speech production. >> hello. how are you? that's the kind of speech that we think allows babies to mirror what they ought to do. >> reporter: so in the interest of brain development. >> hi. >> reporter: i make sure my little guy gets an earful of parentese daily. >> hi, my precious. >> reporter: besides, who could resist? linzie davis, abc news, new york. >> oh, that baby is so cute! so true how they tell you say don't talk down to your baby. and they absorb language. especially around 2 years old. >> there's a fine line between baby talk and babble. you don't want to dumb it down too much. >> absolutely right. it's true. coming up, the world's largest yo-yo, so big it needs to be hung from a crane. and why mcdonald's has become a hot spot for some brides and grooms. that's ahead in "the mix." there's a lot to talk about there. stay with us. cdonald's has become a hot spot for some brides and grooms.