Sailing school capsized at mouth of Santa Cruz Harbor, California, on Sunday
Video captures surfer and marine units pulling 12 children aged 7-12, to safety
Sailor Linden DesJardins, 12, said it was 'scary' and 'very, very stressful'
DesJardins family want to find surfer 'Sean' to thank him for rescuing Linden
Accident was caused by a massive swell that crashed the boats 'like dominoes'
Children on 50F water despite a high surf warning of 25ft 'king tides' on coast
Meanwhile a search is underway for a woman swept out to sea at Pescadero State Beach and a San Jose man in his 30s missing off Point Bonita