Its fun! And I show the kids and parents what I'm doing, which tools I need to do it, etc. Its mostly simple stuff too, like adjusting tension on a brake, set screw for the limit on the derailleur, or patching a tube and pointing out to not forget to check the tire before you put the tube back in. More annoying tubes (or if I'm out of patches) I pop into a small bin to patch later, I have a couple spares for 20" (kid size), including the ones I patched up since the last time.
I also really like that everyone kind of learns that these tubes are for everyone, you won't necessarily get the same one back, and it really doesn't matter because you've still got a working tire again. Good for the kids to learn that it doesn't matter, and honestly good for some of the parents to learn that too.
Since I started doing it another dad has been learning too, and started doing the same thing. Though anything he's not sure about he tells them to ask me.
Plus a really good way to meet a lot of the people in the area, I like doing it