Tree balloons inflated with helium. You can keep them tied, or you can let them go fly in the sky so that they can travel the world, riding with the wind. This drawing that I found on Open ClipArt is very realistic: the balloons are translucid and there are shadows and highlights that will be applied on top of the patterns you use to color them. In addition to the background, there are only 3 zones to color, which makes this coloring page very suited to small kids.
More coloring pages on the same themes:
Themes : Coloring pages, Toy, Balloon, Simple coloring pages