The cow are gets a single capsule (either a single alnico magnet or a plastic capsule with smaller ferrite magnets in it, but the same size) about the size of your thumb. It never passes from the first chamber.

The Buckyball magnets are rare earth and much stronger than cow magnets. A kid who swallowed one might follow it up with another, or some bit of metal, after the first magnet entered the intestinal track and those two might snap together and cause damage.

I think the problem is there whether it is a buckyball magnet or a stack of discs for some craft or hobby. Kids love those kinds of things. You just need to watch them like hawks and be careful what you leave laying around.