Why didn't they leave?
I know that they were waiting for the father and that it was their home.
But I'm sure people in US, 1983, were well informed about the effects of radiation and that it would make sense to leave as soon as possible. And when people are dying around them that would be obvious. They even had radio contact with several places. I'm sure they could have a much better spot for surviving. In my opinion the mother kills her children by staying there.