My son once had a finger-sized "super-strong magnet" "toy" which he took everywhere and used on absolutely everything he could find. He once put it on a TV screen somewhere and it permanently distorted the cathode ray tube. The picture was skewed with weird colour patterns that didn't go away. (It may have been one of our TV's, or a friend's, or it may have been in a hotel room. I forget now.) I know I didn't say anything about the TV, but I quickly confiscated the magnet after that. Those kind of magnets should not be on sale for children but I believe there a few restrictions, and that you can easily buy even larger, even more powerful magnets. Put it next to computer hard drives or next to grampa's pacemaker???
PS. I've since learnt that those magnetic effects on old CRT TV's don't last forever, and in any case, they can be degaussed with a degaussing coil. Makes me feel better now that I never confessed about it.