Thanks everyone, looks like I'll be buying some extra heavy craft magnets so I can hang these on the refrigerator and give some to the grand kids.
Diane
I found some extra strong magnets at the craft store and they work very well. The thin magnets just weren't strong enough.
I've used button magnets and fixed them with hot glue. Works well on the fridge but not on a radiator. (The glue melts when the radiator gets hot!)
I have good luck with the magnets that come on a roll but if they don't work try some double sided tape