RE speed, stock Tamiya 540 brushed motors are not considered fast, but certainly are not slow, especially for a kid.
Most controllers (transmitters) will have some sort of adjustment, so you can tune it to only dish out part throttle until they master it, then turn it up little by little until full tilt, then you will be looking at upgrading to faster motors, etc.
Age dependant, but building is great fun.
RE speed, stock Tamiya 540 brushed motors are not considered fast, but certainly are not slow, especially for a kid.
Most controllers (transmitters) will have some sort of adjustment, so you can tune it to only dish out part throttle until they master it, then turn it up little by little until full tilt, then you will be looking at upgrading to faster motors, etc.