Thanks to Baby Einstein (I would never buy it, we watch it for FREE on YouTube) our 18-month-old twins can now sign:
mommy, daddy, baby, ball, bath, story, eat, drink, kiss, blanket, milk, stop, no, cereal, thank you
We've been teaching them some since they were about six months old: more, all done, please, night-night, and those they've known for quite some time. The rest they've learned over the past week, and have seen only two or three times... and are pros!
PLUS (two bonuses)
#1 - Ayara gets to overhear/see them learning and absorbs it [I think]
#2 - It also includes a Spanish round of words!
If you want to watch just search Baby Einstein - Learning English on YouTube