We love ASL!
I, too, began signing with my kids as infants. With DD I didn't intend to *teach* her, just expose her to my Deaf friends and not make accomodations for her. (I'm a *retired* interpreter, I've been signing myself since age 10, professionally interpreting since 16) At 18 mos, she came to me with a closed mouth and gestured for me to sign to her without speaking
She is now pretty fluent at 6. DS was *taught* to sign, as he was soooo frustrated with not being able to speak but had a strong drive to communicate. We started with nurse (I used the baby sign for water), drink, eat, more, all-done, all-gone, cracker, mom, dad, help me (which is actually a fist planted on an open palm and directed to oneself ~ the help described above sounds like the sign for happy??) ... I can't think of the others right now, but it has blossomed to smooth communication with Deaf people and a great way for me to communicate with them in high stress situations without raising my voice 
I'll try to describe some of the signs requested:
Mom: "5" hand, thumb on chin
Grandma: move "mom" sign outward
Girl: rub thumb of closed hand down jawline
Dad: "5" hand, thumb on forehead
Grandpa: move "dad" sign outward
Boy: "puppet hand" like you're grabbing the bill of a baseball cap on forehead
(female signs on lower part of face, male on upper)
Happy: open palms on chest in an upward movement (big smile)
Sad: open hands drawn down the face (sad face)
Scared: open hands on chest, shaking inwards (scared face)
Excited: "5" hand with middle fingers pointing inward to chest and hands alternating up, fingers tapping chest (excited face)
The baby signs are examples of how children modify ASL, we should, as adults, model the appropriate ASL sign (if you're teaching this as a language, not necessarily if you're aiding communication temporarily) and the children will modify the sign to their ability ~ they don't have to be perfect! My friend's daughter began signing my children's names (I fingerspell them instead of assigning a name sign) by just wiggling her fingers and pointing, now she gets a few letters in there, as her ability to form them has increased: Hannah now looks like H (wiggle wiggle) N (wiggle wiggle) H, and Hayden is H (wiggle) Y (wiggle) N; before long she'll get all the letters in to duplicate the whole handshape of the word

Heres a great animated dictionary http://www.bconnex.net/~randys/index1.html edited to fix this link






There are as many signs for this as there are made up words 
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