The process of using the left (or "non-dominant") hand to index children or siblings in a family is called "ranking." You introduce the children from oldest to youngest. If there are three children hold the left hand in a "three handshape" and start with the thumb. If there are four children in the family you use your index finger through pinkie. If there are five or more, you start with your thumb and work your way down. If by chance you happen to have more than six children, for the sixth through ninth child you make the number on your left hand. What is cool about "ranking" is that you can use the fingers as referents. After you've established which finger represents whom, you can point back to that finger to indicate the person or add more information about the person.
Example of ranking:
HELLO
I "K-E-L-S-E-Y S-M-I-T-H"
HEARING I
MOTHER FATHER DEAF
FATHER NAME "B-I-L-L"
MOTHER "B-E-L-I-N-D-A"
HAVE TWO BROTHER ONE SISTER
[Hold up your left hand in a "four" handshape, palm facing back, arm held at a comfortable angle, keep it there.]
[Touch the tip of the index finger of the left "four" hand with the pad of the right index finger of the right "one" hand.]
BROTHER, "L-O-G-A-N," HEARING, MARRIED, 2 CHILDREN
[Touch the tip of the middle finger of the left "four" hand with the pad of the right index finger of the right "one" hand.]
ME, SINGLE
[Touch the tip of the ring finger of the left "four" hand with the pad of the right index finger of the right "one" hand.]
BROTHER, "F-R-E-D," DIVORCED, ZERO CHILDREN
[Touch the tip of the pinkie finger of the left "four" hand with the pad of the right index finger of the right "one" hand.]
SISTER, "S-A-R-A-H," DEAF, SINGLE