If looking for lowish cost, and fairly simple, my friend Erik Kondo has made (w/ help from me and others) some neat carts starting with a Swagtron 'off-road' hoverboard, and a bolt on 'cart conversion' kit made for kids... Suitable for paras w/ reasonably small butts
and good use of both arms...
We beefed up the front wheel a bit, and added some better foot support frames with straps to keep the users feet from bouncing out... We also replaced the little flimsy seat with a plastic bucket seat with some cutouts for the two control arms, and beefed up the hardware that fastened the cart to the hoverboard...
Result was a 3-wheeled cart that would do about 15mph, controlled by two levers that tilt the HB sides back and forth.... (true 'tank-steering')
It's enough fun that when we let AB's try it, we have trouble getting them off it so us gimps can have a go...
(Search for Erik Kondo to find videos of this and other toys we've built)
ex-Gooserider