The report on low birth-weight babies was published in the journal Pediatrics.

Experts say the first three years of a child’s life are the most intensive period of language and speech development. This is the time when the brain is developing. Language and communication skills are believed to develop best in an environment that is rich with sounds and sights. Experts say children should repeatedly hear the speech and language of other people.

America’s National Institutes of Health says evidence suggests there are important periods of speech and language development in children. The ability to learn a language will be more difficult if these periods pass without early contact with a language.

The first signs of communication happen during the first few days of life, when a baby learns that crying will bring food and attention. Research shows that most children recognize the general sounds of their native language by six months of age. By that time, a baby usually begins to make sounds. These sounds become a kind of nonsense speech over time.

By the end of their first year, most children are able to say a few simple words, although they may not understand the meaning of the words. By 18 months of age, most children can say between eight and 10 words. By two years of age, most children are able to make simple statements. By ages three, four and five, the number of words a child can understand quickly increases. It is at these ages that children begin to understand the rules of language.