About caring for the child.... I don't think it was so much that he cared (more than a normal human being would anyway), but that he didn't want to listen to the old woman wail all night.
You guys are too black and white on these things. There is middle ground. He really believes the girl can still be out there because he did it as a kid. He also probably understood the mother's pain. There is an area where he doesn't care as much about the girl as she does but he understands how destroyed her mother probably is without knowing. It's the not knowing that is the problem. He's right about one thing. In that area of the country the girl could be holed up in any number of abandoned houses, shacks, sheds, barns, etc. The weather is not going to kill her so she can stay there for quite a while if it's free of zombies.
Isn't that what I just said? (note the anymore than a normal human would bit.)
Actually, in this type of genere, it's the Gray Area that will get you killed. Look at any zombie movie, comic, or hell any horror story in general. There is a terrible thing going on and everybody is managing just fine, until one of three things happen:
1. Somebody does something completely irrational because they let their emotions get the better of them.
2. Somebody bases their actions on faith instead of logic/science/common sense.
3. Somebody does something that is morally unforgiveable, like murder, letting somebody die that they could have saved ect..
After one of those three things happen it's a downward spiral of piled up bodies until only a couple remain, the few that never did one of the three things.
It happend in all the dead movies, it happens in all the slasher flicks, it even happens in the Walking Dead comic series.
So keep that in mind when the zombie apocalypse hits... become an athiest, stay calm and rational and always be a straight arrow.