If you haven't already seen it, take a look at the Number Family Diamond and Fill-In set in my store. The description there will help you understand the use of these cards.
For added reinforcement of number families (and fun), here are actual domino cards, with the same colors as the dominoes (at least the ones I have). The sum is printed on the back of each card. Since subtraction is the real test of whether the families are known and understood, an activity that can be done with the domino cards is to pull all of the cards with a particular sum (e.g. all those with “12″ printed on the back), fold the card back half way to reveal one set of dots from the opposite side (e.g. 4 dots), and ask the student how many dots must be on the hidden face of the card (in this case, 8). PRINT in COLOR 2-SIDED ON CARD STOCK. Instructions for doing so are on page 1. These are so much fun!
Susan, Morris Tutoring Productions