I don't think they are the fittest of the fit. Mostly luck that made most of them survivors in the first place. Rick was in a coma, for goodness sakes. Hershel kept walkers in his barn.

Whether it is in the ZA, today, 50 years ago, 200 years ago, or 10,000 years ago, you can't protect your kids from every little thing. Letting your kid play 50 ft away while you stand guard with a gun on top of a trailer seems reasonable to me, unless you think they should spend 7/24 locked in the bathroom. Pioneer families had to let their kids have some leeway, even though there could be Indians, outlaws, bears, and rattlesnakes around. Not every kid survived, but most did.

We don't know for sure she shot the Gov in the brain. So maybe he will show up as a walker.