I think that's the problem, if you give them enough time to focus on it, they'll figure out anything. If you just put them up, and don't make a big deal of it they'll try for a little bit and if it doesn't work right away they'll move to something else.
Not my kids, they don't give up easily. It took my 2nd kid a few weeks till he figured it out.
I had to buy a light cover that the only way to turn it on and off is by sticking a thin stick into it. Even that they eventually figured out but its much harder for them to do it