[sanelss]

To a degree, mentors are certainly there to babysit(in the sense that there needs to be an adult around, you can't just leave a bunch of kids unattended while working with potentially dangerous equipment).

I can't speak for all of them, but I think mentors already give as much as they can. If they have other obligations or simply just want to call it a day for whatever reason then that should be respected. If you've already tried talking to them about it and they can't fill that need for the team then try to explore other options like finding more mentors or just dealing with the situation as best you can.

I can't say I know your teams situation but when I see kids just screwing around most of the day(or most of build season for that matter) instead of doing the things they were supposed to be working on then the last thing I'm going to be doing is staying longer than I planned on.