Do alot of the same stuff they did, but instead of an electric motor, go get a 50cc pocketbike engine and toss it in the back with a half gallon gas tank and use gokart wheels and tires.
I don't know which I like better, the modded car or the fact the son appears to be so involved in the build! Write down that kids name, I bet we see it again...
Pretty awesome video and great video editing skills! Your son has an excellent start at paving the way for the next generation.