I really like ceiling fans (big fan!) and we have them in most of the rooms of our house. About a year ago we also built loft beds for the older two kids bedrooms:

Which offers a potential conflict: you don't want people and spinning blades to occupy the same place. While in that picture they look close together, they're not actually that close: when climbing up and down normally there's a good bit of room between you and the fan. But if you turn around while on the ladder and start playing, you can get into the path of the fan.

While our kids are used to this, they also have friends over. We tried having a rule that the fan needs to stay off when friends are over, but it didn't work very well: they'd forget or a friend would flip the switch. After one of Lily's friends got bonked (they're fine) we decided to make a guard for it:

The idea is, it's easy to see and avoid a bright colored piece of wood, much more so than an off-white spinning fan blade. And if you're on the right side of the wood then you're away from the fan.

Lily and I made it together: we measured the angle, cut one end on the miter saw, measured again, cut the other, sanded, painted, and put it up. When she got bored I did some of the steps while she played elsewhere. We did ~30% of the work together, which was ~60% of my time on it.