Another possibility if you have drop ceilings in your classroom is to allow the kids to paint those panels. (you can cut paper to fit and then just insert into the panels if you want them to not be permanent). The art class at my kids' elementary school did this about 8 years ago, and they are still up and look wonderful!
I'm not sure you'd want to do this lying on their backs! Maybe as a summer VBS project , camp or mid-week activity!
Jaymie