Threw this together this weekend and gave it shot. Alot of fun. Needs foot rests and the ability to steer. Since this was just a prototype, the next one will be better and then I have to build one for the kids to use.
I drilled through the piece of 4x4 for the rear axle and used a 9 mm bolt on one. The 4x4 has four holding screws and glued with liquid nails.
Had to stack to atop one another to get the propert height. There is a hollow axle in the wood with the QR.