Thanks Heather and Magic banana!
installed Minetest and Celestia. I will show him tonight! He has played
Minecraft (installed it on a Rasp) and he loves it so I'm sure he will be
pleased.
He likes platform games so I showed him Commander Keen. I found Clonekeen as
a replacement:
http://clonekeen.sourceforge.net/?nav=sshots
He also likes to play games from the Lego site, but they are all flash based.
On this age they will play what you give them so luckily I still have some
influence ;-)
My Daughter likes those games where you can dress a doll, but also puzzles
and coloring. I think Tux Paint and gcompris will fill that gap nicely
0AD is perhaps a bit too difficult, although now I have a new game to play
(loved Ages of Empires when I was young)