My oldest boy has the Diamond Razor Edge and loves it. Grip is not wide and fits him comfortably.
Youngest boy outgrew a PSE Spyder and is now the proud owner of a gently used Mathews Outback w/ 40#-50# limbs and 26" dl. While adjusting his dl on the Outback is not as convenient as the Razor Edge, swapping out a cam to lengthen dl is not a big deal.
We were looking at a Misson Riot for him and shot one down at the Pro Shop. Very smooth pulling bow and he liked it, but the price was right and condition was excellent on the Outback we found on AT. Came with the 26" cam and I picked up a 27" cam over there since he's growing so fast.
You might check to see if you can change out the grip to one that fits him right if you find a bow he likes. Lots of makers: Shrewd & Torqueless are a couple of the bigger names and have a huge selection of grips in numerous shapes to fit just about anyone. I would be more concerned with the bow, how it fits him, how it pulls, ease of adjustment for dl & dw, and how he shoots it before worrying too much about the grip - you can always change it.
http://www.torqueless.com/http://shrewdarchery.com/home.php?cat=249