What about an ongoing birthday balloon service?
Have the children create artistic cards and then students can place
orders and have a card and fun balloon delivered to the classroom.
(this might get complicated, i dont know...)
Chalk walks. People can pay a small fee and bring supplies to "paint"
or "chalk" a 5'x5' square of their choice. Or have the event be free
and sell t-shirts that a student/students design. Only problem could
be weather, but these events are usually very popular and can draw a
large radius of people. Some travel all over the place to attend these
Interactive Multimedia Artist