I lost the pictures, but when we went to the Pioneer Day parade in Ivins, Utah last summer, there was, in the parking lot next to the inflatable slide that got so hot in the desert sun, kids would come off it in toasty pain, like they'd just ridden the tortilla machine, anyway, there was an awesome, busted-looking train ride. It was a string of cars cut from 55-gallon plastic barrels, with some 2x4's wedged in there for the seats, all pulled by--what else--a 4-wheel ATV.
Which makes The Speedster from American Speedster like the 7th or 8th kid's car I've seen made from a 55-gallon plastic barrel. And it's by far the most advanced, thanks to the addition of about twenty foot of PVC pipe, .
Though it's target demographic is quite narrow--kids who "are to old for the "Barbie Jeep" and not quiet ready for a HUMMER"--you could easily adapt it to your own barrel-and-pvc pedal car needs. And anyway, by the time the kid gets his drivers license, no one will remember what the #$*%( a Hummer is.
American Speedster sells the plans to build your own 55-gallon barrel pedal car for just $18. That price includes help sourcing the discontinued parts the plan calls for. Or you could just get out the electric knife and the heat gun and improvise.