Place all of the cards face down. Have the children take turns turning the cards over two at a time, as in the game concentration.
Have the child call out the sum, product or difference -- decide which ahead of time. For a younger child, you might only use addition and subtraction, while with older kids you can do multiplication. With advanced kids, you can turn over a third number and have them multiply again.
If the child gives the answer correct, she gets to keep the two. Whoever has the most cards at the end of the game wins.
Separate the cards into two equal piles and give a pile to each of two players.
Call out "add" or "subtract" (or "multiply" for older kids), signalling the kids to turn over one card from the top of their piles.
Give the two cards to the player who gets the right answer fastest. Whoever has the most cards at the end of the game wins.
Shuffle the cards and put the deck face down on the table.
Have kids take turns taking a top card off the deck and placing it face up in front of them.
On all of their next turns, they can another draw a card, then look around the table to see if they can find a way to use one of their cards in a division problem. For example, if a child has a 3 and there is another 3 and a 9 on the table, she can make the problem: 9 divided by 3 equals 3. Have the kids collect all of the cards from their division problem and set them face down next to them.
Play continues until all of the cards from the deck have been drawn. The child with the most face-down cards wins.