Hard to argue that it's open source...

Graphene should qualify. That would be a good incentive for kids to learn to root a mobile device and run graphene on it.

I used the web based installer and it was so easy that we would be complaining the kids are not really learning anything by doing it!

You actually don't root a GrapheneOS device (sadly, imo, but this is one of GrapheneOS's peculiarities. If you want root, Lineage is your friend.)

AOSP itself shouldn't be.