Along with sentence construction, grammar is another pillar of language development. At some point between the ages of 2 and 5, kids will add prepositions and conjunctions such as "on" and "that" to their sentences. They'll master the tricky rules of pronouns and differentiate future and past tenses. Making mistakes is how children fine-tune these skills. For example, when a child learns that -ed indicates the past tense, you might hear sentences such as "We wented to the store."
Don't be surprised to see your child's vocabulary grow exponentially through her first few years. This is because her growing brain is biologically programmed to absorb new information. "Between ages 2 and 3, it takes very few exposures to a word before children start to use it in their own speech," Paul says. It's a process called fast mapping. In contrast, "Imagine how many exposures it would take us, as adults, to learn new words in a foreign language."
Fast mapping does have its drawbacks, especially if the process helps your child pick up a word he heard you howl out when you slammed your finger in a drawer. "Try not to react or respond to inappropriate language," Paul says. "If they get a huge response, whether it's negative or positive, they're more likely to repeat the undesirable words."