A yo-yo. Why? Because they know it looks like fun, but they have no idea how to use it. And that’s expected, since many adults can’t yo-yo either. So, a preschooler is left to just told the string and watch it unroll once. Then they will ask you to roll it back up. Then they will watch it unroll. Then they will ask you to roll it back up again. Then they will watch it unroll. Then they will ask you to roll it back up again.

Repeat indefinitely.

If they tire of that game, they will probably try to play with the string in some way. Which always seems to involve stretching it across their face or around their neck. Or maybe chewing on it. So, as you can see, yo-yo’s are both maddening and unsafe. Spread the word.