There is actually quite a lot of information out there about powering up
your Power Wheels.
I have been looking at some with thoughts of (nearly) my three year old
grandson's little Jeep.

Here's just a quick link
http://www.modifiedpowerwheels.com/

If you google, you can find a TON of information, enough to overwhelm you.

BUT they may want to wait awhile so as not to reward him for throwing a
hissy fit.
Maybe give him some little jobs that he can do to earn a new one and some
upgrades.

Kate