I don't have a Nightstar but have played with them. The magnetic reed switch is sealed inside the light. On the outside of the light there's a little slide switch, except instead of moving an electrical contact, it moves a little magnet that opens and closes the reed switch through the sealed plastic. That setup is common in dive lights and I think a kid should be able to operate it reasonably easily, once s/he's developed enough coordination to manipulate small objects.

I don't understand the issue of a deadman switch. Nothing bad happens if you forget to turn off the Nightstar, that's part of the point. It stays lit until the internal capacitor is discharged (several minutes). Then you recharge it by shaking the light up and down.