I'm planning to set up an old laptop with Linux for my 7 and 5 year olds, so I'm curious if you have any other software suggestions in addition to GCompris?
There's plenty! Try `childsplay`, `pysiogame` for collections of didactic activities. Other fun individual games are `raincat`, `colobot`. Try `rabbit escape` also. For fun (we let them play as prize) try `X-moto` and `SuperTuxkart` as well as `Supertux` platformer. We only let our kids play with libre games, so that we are able to adapt the games and learn how they are made, even reuse the assets. My kids are the same age 5 and 7.
The Sugar version of Turtle (can't remember the exact name), TuxPaint (which is also part of GCompris, but runs separately). Edubuntu has some other ideas.