In the bath
Finish that tune
How to play: When your baby's splashing around, start singing her favorite song (it doesn't matter if you sound like someone from week one of the American Idol auditions). Right before a word or phrase that's repeated a lot, stop singing and wait for her to fill in the rest -- even if she just babbles and coos.
Why babies love it: Just like us, little ones like to have their turn -- and your excited reaction when she chimes in is all the encouragement she needs to feel a sense of pride.
What it teaches: Communication skills. "Even if your child can't verbally fill in the word, her brain will be making the connection, forcing her to draw on her memory to try to find the word," says Dr. Perlmutter. By giving your child a chance to respond, you're building the foundation of conversation.
When to start playing: 8 to 12 months, when a baby's sense of how to communicate is growing at warp speed and she's on the verge of uttering her first word.
How to play: Give your baby a few plastic measuring cups or bowls and let him scoop and pour water from each. Next, you scoop and pour over his head (not his face, though) and body so he can feel the difference in how much water comes out of the different containers.
Why babies love it: This gets them going in the same way that plucking out every last tissue from the box does. "When a child realizes that something he does can make something else happen, it's a powerful feeling -- especially considering that he's been completely dependent on you up to now," says Lerner.
What it teaches: Visual-spatial skills. It might seem like your baby's just having a good time pouring water on everything from his tugboat to the bath mat outside the tub, but scooping and pouring water from different-size containers helps him understand the concepts of "bigger" and "smaller" and enhances his understanding of size and shape.
When to start playing: 6 to 9 months, when he has the hand-eye coordination to scoop the water and dump it out and can sit up in the bathtub while doing it. (Just remember that no matter how well your baby can sit up on his own, never leave him alone in the bath.)