Ohh how fun! We have tangram game (2x) and my son it's not really interested in it...But he was for a while, still it was too short.
I might give it a try as well, in the next few days. I still apply that "toys rotating method" on our shelves so I'll switch some things and introduce again tangram.
My son do Math all day, in his head (algebra mostly). So I don't really work on it :)) But from time to time, what I'm working on its geometry (kind of what you do with your children here) but I did little activities lately on the theme so I can't really say that I keep him engaged in these kind of activity.
I guess I just need a plan asap in the future. For now its random...
But tangram and puzzles with shapes and stuff like that it's what I have in mind myself...