Building a Kid's Self Bow
I love to make kid's bows. They are easy to make and make use of small or flawed pieces of wood that won't make a full-size adult bow. Don't get me wrong, you should be just as thoughful about making a nice bow for a kid as you normally would but design can be seriously overbuilt since they often shoot very light arrows at short ranges and kids aren't nearly as worried about performance as adults are.
I make all my kid's bows about the same way.
48-52" in length
1" wide for maybe half the limb tapering to 1/2" tips.
This design fits just about any kid since even smaller kids can pull 12-14" and about 12-15#. The bow grows with the kids since the bigger they get, the farther they can pull, the higher weight they can handle. They are overbuilt enough to go all the way to 24" which puts the weight in the low 30#'s. I always use osage since it's about the only wood I use anyway. I'm sure quality hickory could handle the same design in the same way. Other woods may need to be wider. The wider they are though, the thinner they usually end up, and the harder to tiller in my opinion. They are also more prone to damage and breakage. Kids are tough on bows. Just watch 'em at a shoot sometime :)