Butterfly wallpaper is the lightest way there is to put something living on a wall, and it works at every scale.
Look for Butterfly Effect by Brand McKenzie, Magic Butterflies by Coordonné and Butterfly Delight by Galerie, from a few scattered wings on a plain ground to a full painted swarm.
Lovely in a bedroom or a hallway, and one of the easiest patterns to give a child's room without it feeling childish.
