While always a risk the fact remains many parents who would like to do better for their kids cannot. Finances are a huge part of that. Taking off some of that pressure means the would-be-better parents can be better.
And for those who would game the system or prove unfit there is CPS. Obviously CPS cannot be perfect itself. Still we should try our best to get as close as we can; individually, as institutions, and as a society.
It is also whether you are so overworked and tired that you cant think of kids problems vs you had time to think through kids behavior and figure out there is an issue. It is whether you are isolated in bubble of own head or whether you get to meet variety of people to understand how society works and have experience with it.
It is whether you are high confidence and mentally ok to discuss issues with kids friends parents, or whether you are low confidence on end of rope generally so you cant (or botches it).
Basically, I don't think it's a given that there will be huge dividends down the line if you just provide free child care to people.