Tall little

I have a boy he's about 6'4 and 250 he loves to be little but it's just physical hard to change him with little to no help from him, I'm trying to keep him feeling little but having him help me takes him out of his head space, does anyone have some advice to making it easier.

Well when kids get out to 3+ yrs old they do somewhat start cooperating a bit to simple instructions like "lift your bottom!" and for a diaper change that's the big one. It's not like you need help with the tapes?

Pump iron and get stronger.

Give him a damn good spanking!