Have the kids draw a crowd of people in an unusual situation, like
having a party in an elevator, for instance. Tell them you want them to
draw everyone's face different, different ages of people, different
clothes, different body positions, and you want their drawing to tell a
visual story. Cartoon style is fine. Emphasize differences and
overlapping, lots of details...keeps them busy, and they have fun. Let
them work on them in pairs for even more enthusiasm.