I make kid bows for that age range all the time. I use a 48"x1-1/2"x1/4" red oak slat from home depot. I glue on a handle made from red oak, 6"x1-1/2"x3/4". I then taper the limbs on the sides from 1-1/2" at fades to 3/8" at tip for a pyramid shaped bow. Shape the handle to about 3/4" wide by 4". Cut some notches with a chainsaw file for string nocks, spray with spar urethane, put on a leather grip(optional) and your done. I buy stings made for 48" recurves and they work perfectly. These bows usually end up at 12-15# @ 20". Total time per bow is about an hour of actual work. String $10, wood $3, expression on an 8 yr olds face as he stalks a chicken; priceless! Lol, he wasnt suposed to do that