I don't think it's a stupid idea to redesign how schools work. Why just shoot the idea down rather than consider the possibilities?
As many people have pointed out, a lot of children have to go "somewhere" to be looked after during working hours, whether that's clubs, childminder or whatever so it's not beyond the realms of possibility that this could be done in a school setting.
Obviously nobody wants them to be doing academic work for 10 hours a day, but all those other skills that would be useful - vocational or life skills that could be taught by a different set of teachers - and things like hobbies - music/dance etc. could be done there. A bit like wraparound care, but with actual focused stuff to do, rather than just effectively babysitting?
How do we fund it? Combination of subsidies for low income, key workers, parents, variable amounts depending on the class? It could be an opportunity for people who want to work only a few hours per week. One of those "hen's teeth" jobs that has to fit around timings for the rest of the family. Make it optional so that parents can use it or not as needed?
At the moment there are a lot of grandparents doing child pickup/drop off and afterschool care but our population is aging and people are having children later, meaning that the grandparents are getting older and people are working longer too.