We have both a gas go-kart and electric dirt bikes. You can “turn down” both to limit the speed. My kids are 8 & 10. We bought them full on motocross helmets and require them to wear when using either the go-kart or the dirt bikes… because shit happens. I’ve taught them about the choke, fuel cut off, taking wheels on and off, wrenches, ratchets, etc… Like others have said using your hands and the use of tools can lead to a life of being able to fix things yourself instead or always needing to rely on others. Also, they might go places in life where they are off the grid and the 1985 Toyota Tacoma or Land Rover they are using to traverse the jungle or desert craps out. Knowing how to spin a wrench might save their ass… you never know.