Lead
"She only had about ten words last week. Suddenly she's adding new ones every day." From around 18 months, parents sometimes describe this shift. At the same time, a different kind of worry surfaces: "The children her age are already putting two words together — ours is still around twenty words." Both reactions come from the same period.
Language development is said to include a phase of rapid acceleration often called the vocabulary spurt. But this spurt does not happen at the same time, or with the same intensity, for every child. The more accurately documented fact — worked over for decades in research — is that some children accelerate sharply while others do not. That heterogeneity is where the story actually begins.
This article covers what the research says about the inflection point around 50 words, the move from single words to two-word combinations, and how to read a child who appears to be running a little behind.