Trig Rummy is up in this edition of Math Teachers at Play, a nice way to experience some of the variety of math ed blogs that are out there. It's hosted this time by Homeschool Bytes.
Here's a quick game for young kids up to 1st or 2nd grade. I think I invented it, but it's basic enough that many people have done something similar, I'm sure.
Give Away - It’s better to give than to receive!
Players: 2 to as many as you can stand.
Rules: All players start with five blocks (coins, beads, etc.) For one player they should all be the same, but different from the other players. The goal is to give all your pieces away.
Turn: Player says how many pieces they have. Then they roll a die. Players give away as many as they rolled – except on a 6 they give away nothing. Choose one other player you are going to give your blocks to. The first player to give all their pieces away wins!
Questions: Good questions to ask include “How many will you have left? How many will I have? If you have 4, how many have you given away? I can give back 4 blue, how many red do I need to put in?” Work on counting on and subitizing. Subitizing is recognizing an amount by looking – for example, asking: “Can you tell how many blue beads you have just by looking?” Try arranging the pieces in common patterns, such as on dice or dominoes. For counting on, if the player knows how many of one color (like 3) count on the others (4, 5, 6, …) instead of counting them all from 1. Ask about strategy and try to get players to think about giving to those with least.