There's a pump forum for parents with children using insulin pumps, I would say go for it as have only heard positive remarks about small children using pumps.
So the child isn't inconvenienced by the pump many parents make a pocket for the pump in the back of clothing so it fits snugly in the small of the back well out of reach of small hands.
All pumps have child safety locks on as well so no chance of buttons being pressed to deliver extra insulin or turning the pump off.