7 to 8 hours is probably too much organised schooling, already. However, there's an argument to be made for letting kids stay on the premises in a semi supervised environment after hours.

There's lots of resources available in school which could be useful; you can offer some activities (but please, not an additional 5 hours on top of 7 hours of school), or help with homework (dito), and generally offer an environment that's hopefully more conducive to learning in the broadest possible sense than some of the worst home/street environments.