Someone from Reading Uni doing his PhD was leading it, and I think all the kids from about 8 and up were allowed to join in, though there was no strict lower age-limit; it depends on whether the child is interested and able to participate without ruining it for everyone else, etc. The teacher apparently really enjoyed it :)

There've also been art lessons from a professional illustrator (I think), and there are plans afoot for a writers' workshop. Space is limited though so until the philosophy group stops meeting we need to find more space.