Actually most of the motors used in power wheels are similar to the 550 size motors used in RC. A common motor used in power wheels is a 550 21T motor.
Doing some research. The power wheels battery battery runs 12V 8ah and 120A max discharge rate so, if my math is right it's the same as a 3.25S 8000mah 15C Lipo.
I think it's totally doable but I don't think this is the right combo to use.