We started making a list the other day of all the words the kids know. For the most part, all three of them use them equally, but there are a few words that are still child-specific (though it won't take long for the other two to learn them). We have definitely found that their vocabulary has grown by leaps and bounds once we started them on the "Signing Time" dvd series.
Boom, Book (buh), Bubble (bah-bah), Ball (bah), Butterfly (buh-bye), Bye-Bye, Daddy (dah-dah), Out (aw), All Done (aah), Pacifier (pah-pah), Pumpkin (puhm), Pop Pop
Elephant, Camel (spitting), Dog (panting), Flower (sniff sniff), Clock (tick-tick), Hot (blowing twice), Monkey, Pig, Bear
Book, Eat, Hat, All Done, More, Help Me, Dog, Squirrel, Sun, Bath, Monkey, Frog, Butterfly, Banana, Drink, Fan, Pacifier, Phone, Cold, Stay, Milk, Cat