I love making kid bows. I just made a couple, one for an 11 yr old boy. He is drawing 24#@20", but my 9 yr old daughter is drawing 16#@19". I guess it all depend s on the kid's ability, experience, and so many other factors. 20#@20" is a good place to start.
Don't forget to post some pics when done, we'd love to see it.
Tattoo Dave