FreeGameDev

Gaming on linux mentioned GB Studio. As someone who has a kid who wants to make a game, I took a look. It looks fairly easy to use for something simple. You could create a word that players can explore pretty easy. It doesn't have a combat system. The creator made Untitled GB Game with it. The game includes a pong game inside so you might be able to build a Zelda like adventure game in it but I don't know how easy it would be.