If its a kid who already takes their toys apart, a kit might be good. something like this: https://www.sparkfun.com/products/19520 https://www.sparkfun.com/prod

If its a kid who already takes their toys apart, a kit might be good. something like this: https://www.sparkfun.com/products/19520 https://www.sparkfun.com/products/19520 Otherwise i'd suggest something more towards "programmable R/C", maybe a mini drone and find a software suite that can run it through programmed courses. No idea what that world is now, personally.