I sometimes will take some throw out type of paper like scraps of wrapping paper that actually is huge to a child but you don't want to wrap anything in it. Use the reverse white side, grab some markers, roll it out on the floor and tell your kids to make a mural or just "go to town" on whatever they like! You never know what kind of masterpiece may come of it from your little Van Goghs! :-)
We are lucky enough to have an extra room that we keep an art mat over the top of the coffee table and always have paper, markers, and crayons "ready to roll" for our toddler! We are, of course, art nuts ourselves....so it isn't unusual we should have that! The Childcare Center my son goes to says when they say it is "Art Time" he comes running to the tables! I was glad to hear that! PHEW!