During early childhood, children's abilities to understand, to process, and to produce language also flourish in an amazing way. Young children experience a language explosion between the ages of 3 and 6. At age 3, their spoken vocabularies consist of roughly 900 words. By age 6, spoken vocabularies expand dramatically to anywhere between 8,000 and 14,000 words. During infancy and toddlerhood, young children are almost always able to understand far many more words than they can speak. However, with this language explosion, their expressive (spoken language) abilities start to catch up with their receptive (ability to comprehend language) skills.
As children move beyond using two word sentences, they start to learn and understand grammar rules. All English-speaking children follow a regular sequence when using these rules. For example, children first begin using simple plurals (cats) and possessive forms of nouns (Daddy's car). Then, they put appropriate endings on verbs (jump becomes jumped), use prepositions ("in the street"), articles ("the", "a", or "an"), various forms of the verb to be ("is", "are", "were", etc.), and so on.
In part, the explosion in expressive skills occurs because of the gains in attention and memory described above. Children become increasingly skilled at remembering and practicing the language modeled around them, as well as modifying word use based on other people's reactions. These skills can result in very embarrassing situations for parents, such as when Johnny repeats a swear word or undesirable comment at Sunday dinner at Grandma's that he heard from Dad Friday night. Caregivers should be especially careful not to encourage poor language choices, such as incorrect grammar or swear words, by laughing or making a game of them. Children may view this attention as approval and will often continue to use that word or phrase to obtain more attention in the future. For more information on encouraging appropriate language, see the discipline and guidance section in the Preoperational Stage Parenting article.
Beyond growing their vocabularies, young children start to expand their ability to use different forms of words (e.g., irregular verbs such as "She brought" instead of "She brang") and form more complex sentences. Between the ages of 2 and 5, children also refine their ability to pronounce words. However, they often make up words that they don't know and need. In contrast, school-age children start to speak more like adults; they can recognize basic grammar errors, put thoughts into question form, and begin including negative expressions such as "not coming" into their sentences
As they get older, children's use of language also becomes more mature and complicated. For example, children start to understand the use of basic metaphors based on very concrete ideas, such as the saying "hard as a rock". They also begin to tailor their speech to the social situation; for example, children will talk more maturely to adults than to same-age peers.
During early childhood, children's ability to understand language at a more complicated level also develops. Young children develop "Illocutionary Intent", or the ability to understand that a sentence may have meaning beyond the exact words being spoken. For example, with a very young child, Mom would have to say "Jennie, please bring me your cup," for Jennie to understand that Mom wanted Jennie to bring over the cup. With older children, Mom can say "Hmm…I need Jennie's cup so I can fill it with juice…..," and Jennie will understand that the true message is actually "bring me your cup".
By ages 5 to 7, young children can also understand and learn to use a word by being told its definition (rather than experiencing that word directly). In addition, children start to understand that words often have multiple meanings, opening up a whole new realm of humor and jokes that they will find amazingly funny. For example, "Did you hear about the pirate movie? It's rated R-r-r-r-r-r-r" may elicit a stream of giggles from a school-aged child.