Plan ahead and have children bring in special items that they would like to show and tell. Or act out a favorite story. Sing, dance, and be merry. The sillier, the better. And those children who want to just observe can be your audience.
Indoor picnics can be festive and fun.
Choose traditional picnic foods, or just pretend, using a checkerboard tablecloth on the rug. Lawn chairs, sunglasses and beach towels add to the atmosphere.