The way I like to make my kids bows is 1lb drawn for each year of age until they feel the bow is to weak (usually around age 15), and then I increase the poundage. I also make one every year for each kid, on average. I make the arrows very weak in spine and a little long. That way, they shoot right where the kids point them, even if they want to shoot something 2 feet away.
That's a LOT weaker than other guys build 'em, so I'd wait for more replies.
Edit: One more thing, I make 'em as weak as I can for safety as well as for comfort. A kid with a 15# to 20# bow is a scary thing.