Please consider some kind of roll cage if you're going to put a 2-3 year-old into this. In the United States we see a tremendous number of toddlers who are very, very badly injured (or killed) in ATV rollover injuries. Obviously an ATV is a much bigger and heavier vehicle than what you're doing (which is cool) but the mechanism itself of rolling a vehicle over onto a child can lead to a very devastating injury pattern.