What your baby is doing: Though linguists aren't sure why, toddlers at about 19 to 20 months have a "language explosion." After months of slow progress, they suddenly start to learn words at a ferocious rate, as many as nine a day. This is when I stopped writing each new word in my daughter's baby book. The last note in her "new words" list is "Too many to count!"
This explosion of words leads to the exhausting "Wassat?" stage. By the end of the second year, your toddler will be stringing two, or even four, words together in sentences. This is also an age of cute mistakes, as kids overextend and "under-extend" concepts. For instance, your child may learn that the round toy is a "ball," figure all round things must be balls and point to the full moon, and chirp, "Ball!" Or she may think that all four-legged creatures are "Doggie!"
What your baby can understand: Your baby will slowly begin to understand the idea of verbs. Fully aware that you are her key to language, she will watch and listen to you, absorbing everything you say and do.
Things you can do to help: Try to have real conversations, and no matter how brain-dead you feel, answer each "Wassat?" question. It's also important to set a good example. I'll never forget letting a profanity slip as I struggled alone with a car safety seat, a rental car, and a toddler. My almost-2-year-old chirped, "Sh--! Sh--!" for 30 miles until she fell asleep. In hindsight, the incident is funny (I'm much more careful now), but at the time it wasn't cute.
What to watch: Talk to your child's doctor if your toddler doesn't use any two-word phases or answer simple questions by 2 years of age.
What your baby is doing: In the third year, your child really begins to put it all together. He's refining what he's learned so far. He adds "When? Why? Where?" to "Wassat?" He begins to add complex ideas, learning that "no" can mean "not" or "don't" or "it's all gone." Late in the year, he may begin to use more abstract verbs like "think" and "know." As his memory grows, he starts to tell short stories. As he gains control of the tip of his tongue while speaking, he begins to manage sounds like ph, th, and r.
What your baby can understand: He will begin to understand tense and plurals and suffixes such as "ing" and "ly." Late in this third year, your child may be able to tell short stories.
Things you can do to help: Rhyming games help build awareness of language sounds. If he makes a mistake, repeat the sentence back correctly instead of drawing attention to the error. For instance, if he says, "I goed playground." You can say back, "You went to the playground? Great!" Add storybooks with more of a narrative. Kids need more assistance than we do for conversation. Take a look at his preschool class list, and start making stuff up. Was Mary in school today? Add something silly, like "Was she wearing that hat with the fruit on it again?" See what happens -- you may find out what's going on.
What to watch: Kids' thoughts may outstrip their ability to form words. My daughter stuttered a little when she was 2 years old. It passed. If stuttering, or some other problem, like a lisp, concerns you, consult your pediatrician.