A water balloon with a glow stick on the inside, in a stocking, hung from trees, patio cover, or the ceiling. Same pin elsewhere said: "Put a glow ball in a white stocking and hang many from trees or the ceiling." But what are glow balls?
Could be cool ice cubes for Ice Cave: making light boxes for stage sets out of air filters and duct tape. Would be neat to use patterned or colored duct tape. Maybe try spray painting or dying the filters for colored lights?