5 to 7 months
When your baby begins to add in consonants, it means she's now able to produce a full repertoire of sounds--a major linguistic milestone. "It's harder to produce consonants because they require interaction between the tongue and the lips," says Roberta Golinkoff, Ph.D., director of the University of Delaware Infant Language Project in Newark. "It's a big deal."
What to say back: Narrate the sights you see on your drive or your daily plans ("We're going to the store for some milk, and then Daddy's taking you to the park!"). Talking to a non-talker may feel bizarre, but research has found that infants actually understand far more than we realize. In one study, 6-month-olds who heard the word "mommy" responded by looking at a picture of their mom.
7 to 9 months
Was that a first word? Hmm? Though your baby is probably still simply parroting sounds, once she starts babbling in distinct syllables, her "conversation" can sound so much like language that it's hard to tell. Consider this her final dress rehearsal for putting those syllables together in a way that has real meaning.
What to say back: Talk about the things around her so she'll connect objects with words. Just don't assume "bo-bo" means "ball" if she says it while reaching for her shoe. "Notice where your child is looking before you label an object. It's very adaptive for babies--and a lot of parents do it naturally," says Jenny Saffran, Ph.D., director of the Infant Learning Lab at the University of Wisconsin-Madison.
9 to 12 months
Getting out just the right sounds takes practice, so for now, your baby's making up combos that indicate real objects--a halfway point between babbling and true speech. She may say "nee-nigh" for "bottle," or "sho-sho" for "yogurt," for example.
What to say back: As long as you know what your baby's trying to say, don't quibble over correct pronunciation. Swapping in weird names for regular words is normal for new talkers--so your best move is to respond in a way that shows you understand: She says "banktee," you produce her blanket. It's cute to hear (and say) her made-up words, and experts say it's fine if "banktee" becomes de rigueur in your household. Eventually, you'll phase it out for the real thing.
12 to 15 months
Whatever recognizable word your child produces first, it's bound to be something she's fascinated by and something she can easily say--which is why the single-syllable "Da," "Ma," "ball," and, yes, "dog" are fairly common first words. "Kitten" and "television"? Not so much.
What to say back: "Hurrah!" Cheering on her speaking attempts will motivate her to master new words. Plus, Golinkoff notes that the rule for babies learning to talk is "the more language in, the more language out." So keep chatting! By doing so, you're supplying the words for interesting objects and emotions. Add that to praising her for using the ones she already knows and you'll soon have a total motor mouth on your hands.