My six years son and I are playing boardgames a lot. Why? First, it's fun. But it's also a very good tool to learn. Following experimentations I made with my students (
http://chroniquesdufortbastiani.blogspot.fr/2014/03/fun-learning-games-learning.html), I play with my 6 son to help him learn things (like addition, subtraction, strategy, etc.).
Okko is a very simple and fun game to do that.
But we also play
King of Tokyo (with no change to the rules),
Mice & Mystic (I've simplified the rules),
Galaxy Trucker (I've simplified the rules) and
Stratego (with no change to the rules).
And next year we'll start BattleLore...