People don't need to be forced to feed themselves and their children, whether they care enough to be bothered about it or not. That's because if you don't eat, you die. Unless the parents are unbelievably callous (which does happen, but only very occasionally), they will do whatever it takes to keep their children fed. So the problem of parents simply not caring enough almost never arises.

By contrast, if you don't send your kids to school, they don't die – they just grow up to be useless people who do nothing but hang around causing trouble for everyone else. Then they can't get a job, so it's either benefits or crime, and the economy goes (even further) down the toilet. Unlike with food, vast numbers of parents wouldn't care enough about education to make their children go to school, or to pay for it in the first place.

Don't you think preventing all that unemployment and crime is worth spending public money on?