Rainbows are everywhere in design right now — from sneakers to bath mats — and the whimsical theme is perfect for a toddler’s room. We love this giant, peel-and-stick decal from Pottery Barn Kids. You can use the rainbow arch to bridge awkward corners in a room, such as the space between this nightstand and bunk bed. Or you could use it behind a regular twin bed to create a faux headboard.