"Always step up into the liferaft" and "always stay with the car" may be right 90% of the time, but aren't always right.

In this situation, they weren't reported missing until 5 days later, and the search area was huge (~100 miles x 50 miles). If they didn't get the chance ping off the cell tower and their family didn't have the monster $ to pay for private helicopters to search for them, they might well still be out there. You can typically count on 3 weeks without food for an adult, but maybe not for young childeren.

I would have walked out too. It would have been better to walk out sooner - seven days of no food and high stress doesn't increase your strength or reasoning ability.