My 5 year old is in the 5% for height and weight so he's just a little dude and he needs the smallest drawlength possible and the physical weight of the bow makes a difference for him too.
My 7 year old is at 50 percentile so he's average and he prefers to shoot the mini genesis too. I did not try them on the regular Genesis. The physical weight of the Genesis Pro was too much for either of them.
I've got the mini genesis cranked down to 6lbs and the arrows (3L-18 easton hyperspeeds and GT Lightnings fly fine from 12 yds I don't have enough back stop beyond that for them to shoot safely)
If the child can comfortably hold the Genesis Pro I'd recommend that as it has the draw stops (which are adjustable and you can just leave them off too) on it. Keyword is comfortably.
Good luck in your search.
Sam
http://www.genesisbow.com/
The new Mini Genesis features:
• 29 1/8" axle-to-axle length
• 6 1/8" brace height
• Adjustable draw weight 6-12 pounds
• Draw length range of 14-25 inches
• 2 pounds mass weight
• Carbon cable guard
• Four popular flavors (red cherry, blue raspberry, black licorice and camo)
• 77 11/16" string length
• 30 13/16" cable len
Genesis
* Single cam compound bow
* Draw weight: adjustable from 10 to 20 lbs.
* Draw length: 15" to 30"
* Percent let-off: Zero
* Axle-to-axle length: 35 1/2"
* Brace Height: 7 5/8"
* String length: 94 3/16"
* Power Cable Length: 37 1/4"
Genesis Pro
* Higher draw weight - adjustable from 15 lbs. to 25 lbs.
* Larger centershot clearance area - accommodates modern rests and allows for advanced bow-tuning techniques.
* Easy-to-adjust draw stop - all you need is an Allen wrench (provided) to change draw stop positions from 18.5" to 30".