My greatest parenting regret is that I taught my son how to play War.
Don't get me wrong, he loves the game. In fact, that's precisely the problem. For weeks after I taught him the rules, War was the only game he let us play, and it got old fast.
If you haven't played War, it's a ridiculously simple card game. You deal the whole deck out to two players, and then both players flip over the top card. Highest card wins. If the cards are the same rank, both players put three cards face down and then flip over the fourth card. Again, the highest card wins the whole pile. The game continues until one person has all the cards.
The game is entirely driven by luck, and it can drag on for twenty or thirty minutes as one player, deck spilling over with forty-something cards, tries to win those last few pesky cards from their opponent.
To stave off the boredom, I started looking up some variants on War. As it turns out, some of these are really fun! Most importantly, they create opportunities for you and your kid to have a little math talk while playing.