Covert,
Those 125's are great...my friend has one and he's 14 and it's just right for him still(he had it since he was 5). Hes had to change a couple of gears and get new pistin rings and other stuff...and it's still running fine.

I gotta say I think Honda made better quads in the 80's than the 90's.

 

Oh and I think the Yamaha blaster would be good for your son.

 

The KASEA SKYHAWK is 150cc and its looks are like a 400ex but made for younger ages. itll be 4-6 years of fun before your son will want the Honda 700ex :-)

 

He wanted auto clutch