They contribute to GDP spend, but from the fiscal point of view they are a drag. As for actual percentages per country, I think it heavily varies. In EU i think family spending is like 3% of GDP.

The hope is that this drag will either generate higher cash flows later (i.e money spent on education now will allow them to create value for economy later) or reduce outflows later (i.e a child that gets braces and dental health care now won't spend their whole adult life dealing with teeth issues on taxpayer's dime).