ETA: Gwern checked the book and posted the relevant section below. I got it backwards-- seven to twelve are the ages most likely to die. Six and under are more likely to survive.
Actually, there's something rather like that in Deep Survival, a book that's mostly about wilderness survival. IIRC, six to twelve year olds are more likely to survive than adults, and it's because of less fear of embarrassment.
However, the author didn't go into a lot of details about which mistakes the adults make-- I think it was that the kids seek cover, but the adults make bad plans and insist on following through with them.
Downloading the book, pg236, you forgot one interesting detail:
...One of the many baffling mysteries concerns who survives and who doesn't. "It's not who you'd predict, either," Hill, who has studied the survival rates of different demographic groups, told me. "Sometimes the one who survives is an inexperienced female hiker, while the experienced hunter gives up and dies in one night, even when it's not that cold. The category that has one of the highest survival rates is children six and under, the very people we're most concerned about.&quo
Here's the new thread for posting quotes, with the usual rules: