They are fun, especially with the motorized arms, but they are crazy expensive last I checked. There are cheaper options, for Arduino and microbit. But even those are not cheap. They run at at least $30, without the microbit or arduino, for a couple of motors, IR and ultrasonic sensor.
Makey Makey is another fun bit of hardware for kids. Works great with scratch too, have them make their own scratch game then use makey makey to build their own controller