Although speech and language continue to develop through adolescence, children usually reach major milestones in predictable stages by 6 years of age. However, the exact pace at which speech and language develop varies among children, especially the age at which they begin to talk.

Communication skills are often categorized as receptive language and expressive language. Receptive language is the understanding of words and sounds. Expressive language is the use of speech (sounds and words) and gestures to communicate meaning.

Details of the developmental milestones can be evaluated according to age.

• Birth to age 1:
  • Babies begin to process the communication signals they receive. During the first months of life, they are usually able to recognize their mother's voice and actively listen to language rhythms. By 6 months of age, most babies express themselves through cooing with vowels and one or two consonants. This progresses to babbling and repeating sounds. In addition, babies learn to vary their cry to communicate their needs.
  • By their first birthday, babies understand and can identify each parent, often by name ("mama," "dada"). They repeat sounds they hear and may know a few words.
• Ages 1 to 3:
  • After the first birthday through age 2, a toddler's speech and language foundation grows rapidly. During that time, 1-year-olds learn that words have meaning. They point to things they want, and often use one- or two-syllable sounds, such as "baba" for "bottle." By age 2, children usually can say at least 50 words and recognize the names of many objects, including those in pictures. They also understand simple requests and statements, such as "all gone."
  • Many 2-year-olds talk a lot. They usually can name some body parts (such as arms and legs) and objects (such as a book). Not all their words are intelligible; some are made-up and combined with real words. In addition to understanding simple requests, they can also follow them (such as "put the book on the table"). They should be able to say at least 50 words. They usually can say between 150 to 200 words, some of which are simple phrases, such as "want cookie." Pronouns (such as "me" or "she") are used, but often incorrectly.
  • Some children are naturally quieter than others. However, a child who consistently uses gestures and facial expressions to communicate should be evaluated by a doctor. These children are at increased risk for having speech problems.
• Age 3 through 5:
  • More sophisticated speech and language develops from ages 3 through 5. By age 3, children learn new words quickly and can follow two-part directions (such as "wash your face and put your shoes away"). They start to use plurals and form short complete sentences. And most of the time their speech can be understood by others outside of their family. "Why" and "what" become popular questions.
  • Most 4-year-olds use longer sentences and can describe an event. They understand how things are different, such as the distinction between children and grown-ups. Most 5-year-olds can carry on a conversation with another person.