What's the best way to build a baby's (or anyone's) vocabulary?
Talk! Talk about what you're doing. Let's unsnap your pajamas. And pull out your arm. Oh, good stretch! And your other arm. And wiggle those legs right out. I found your toes! Ooo, do you feel cold? It's cold without clothes! All the live-long day, talk talk talk.
And listen! Try not to interrupt your baby's babble. Look them in the eye as often as possible when they grunt or babble. When they pause, respond to what you imagine they're saying. Every baby finds their own rhythm of conversation. When Baby A was only a few months old, I had to interrupt her babble with Ahaa or Niin every ten seconds, or else she would stop. I guess she didn't want to waste her breath if she thought I wasn't following.
When they attempt to say words, validate and repeat the word after they've said it. Example: Baby: [pointing to a ball] Ba! Adult: Ball! [offering the ball] Would you like to hold the ball? This corrects or reinforces correct speech in an empowering way. Avoid "baby talk", as it confuses, and avoid negativity about or scolding for incorrect or delayed speech.
When reading, point to the pictures while you are talking about them. This is particularly easy in picture books with simple plots.
I've always pointed to the telephone, red balloon, bears, chairs, etc. in Goodnight Moon. Ask toddlers to point, such as Where is the red balloon? Ask questions about the pictures, Have the kittens stop playing with the string?
P.S. A bedroom inspired by Clement Hurd's great green room.
P.P.S. Mo Willems' Listen to My Trumpet publishes TODAY! Mo says, "Piggie can't wait to play her new instrument for Gerald! But is she ready to listen to his reaction?" You can run out and be the first of your friends to snag it. Except you won't beat me to the bookstore.