I read this book sometime between 1990 and 1995. I don't remember anything about the plot, characters, cover, etc. -- but I do remember the following episode.
The children made small wooden carts that they could sit completely in side of, which they called tanks, which were steered via a rudimentary system of strings attached to the front wheels. In their neighborhood there was a ravine or valley of some sort. They took the tanks to opposite sides of the ravine, and rode them down to the bottom, attempting to smash into each other.
I remember this anecdote because shortly after reading the book, I built my own "tank" from leftover fencing and some lawnmower wheels. I didn't have a ravine, but somehow I convinced my older brother to push me around in it.
Any ideas what book or story this might be from?