Kids grow quickly, which means the toys they ride must change, too. This modular construction kit allows you to build up to 32 different vehicles — everything from bicycles, to tricycles, to go-carts, to skateboards — for your kids that are all completely self-propelled and surprisingly sturdy. The crowd-funded kits — even the new ePulse models, which use brushless DC motors to inject some power into your peddle —assemble with a simple hex key, and are the perfect weekend project for you and junior. The only downside? You’ll probably have to let him ride it first.