I try to focus this--as you rightly did--on the child. Because it is true that it is, in a sense, unfair that we as individuals have to pay for the results of some bad, lazy, immoral parenting out there in the world. But I think that (1) community interests need to be considered and sometimes do, in fact, trump individual interests, and (2) that it is more unfair that those children are in that situation. I want to fix the kid's lot in life more than I care about the free-rider problem of the parents. I'm always astonished more professed Christians don't feel this way, too.