A fact family is made up of three numbers. Just as in any family the members, or numbers, are related and there are always at least four math facts to be made with them. Take, for example, these members of a fact family: 6, 4, and 10.
In the family 6, 4, and 10 they are related because you can add two of the numbers to get the last number.
6 + 4 = 10
You can also switch the first two numbers, using the commutative property of addition, and still get the same answer.
4 + 6 = 10
Just find how they can relate! Hope it helps!