Before they reach 20 months of age, many children begin to add single words together when they speak. These early word combinations, however, usually don’t follow the rules of a sentence. For example, a child might add words together one at a time, like “man” and “roof” and “bang” to describe a repairman on the roof. While each word has meaning, the combination of individual words does not really develop into a sentence. By around 20 months, children begin putting words together in more meaningful, sentence-like ways. For example, a child might say things like “ride bike,” or “mommy keys.” Some call these early sentences “telegraphic speech” because they contain only critical content words and no articles, prepositions, or pronouns (“the,” “and,” or “with” for example).
Bates, E., O’Connell, B., & Shore, C. (1987). Language and communication in infancy. In Osofsky, J. (Ed.), Handbook of infant development. New York: Wiley.