But your kids would have the freeze response, too, so they'd be just as fucked. I'm pretty sure the whole sacrifice-for-the-herd idea has been dropped by most biologists.

I think it's more a human thing. Our inhibitions take control. We should react by running away, but the want to not look like a coward, not look silly, the want to help and protect others (not the biological need here, but the psychological, societal pressure on us to do the right thing) is perhaps powerful enough to make us not do what our more basic instincts are telling us to do.

Are there animals living in the wild that freeze up like humans do sometimes? I can't think of any, but it would be interesting if there are.

Edit: The opossum seems a good example. The point is not to sacrifice itself, but it does "freeze" as a response to stress. Not that I think these 3 people can be compared to opossums in their behaviour, but it does exist in the wild.