Bad parents wouldn't be so much of a problem if children were considered communal, rather than individual, responsibilities.
While I instinctively approve of licenses to parent, when I think on it I wonder if that might be too counter to human nature to ever enforce successfully.
And my deeper feeling is that it's the "two parents have a kid, so the kid belongs to them" culture that causes a lot of the problems.
Sir, Could I See Your Breeding License?
Most important is that children don't have to grow up under horrible circumstances inflicted on them by the inability of their parents. You always have to weigh the freedom of some against any negative infliction it could have on others. In this case a bit less freedom would guarantee a lot less distress.
It is reasonable. I don't see how we can ask for species-appropriate animal husbandry regarding animals like chimps but not children. You have to have a drivers license for good reasons too. So why is everyone allowed to rule over helpless human beings for years without having to prove their ability to do so in a way that guarantees the well-being of their protégé?
Such discussions always remind me about something important. Children should not be assigned with any religion. There should be a certain age where they can decide what religion they want to follow, if any. This doesn't mean that religious people shouldn't be able to have children but that they shouldn't be able to force their children into a certain framework either. Parents should be forced to allow their children to take part in a educational framework based on contemporary ethics and knowledge. I don't even have a problem with lessons in religion in school as it is part of human nature. But it shall not be focused on any truth value or a certain religion but an overview and comparison with non-religious ethics and truth-seeking.