Step 1: How to do it
1st design shown below: the wood bits are pretty obvious, just sticks and scrap wood. the three wheels are large ball bearing races from some unknown deceased vehicle or machinery. they just whittled down the sticks and jammed the bearings onto them, then nailed the wood together.
operation: to steer, you just lean left or right a bit, and twist the front wheel a bit left or right using the hand grip.
the 2nd design below is a bit narrower and more like a skateboard than the first, the two-wheeled rear-end is straightforward as shown in the photo. the front end has a more complex setup with a steering column - there is a vertical stick which has a perpendicular handle at one end for steering, and the front wheel is mounted at the bottom end of the steering column on another perpendicular stick. note: i'm not sure the more complex steering system here is actually an improvement. the reason i didn't get a good photo is that the kids were afraid i was going to steal their buggy and wouldn't let me near it!