The Naming Explosion
Between 18 and 21 months, toddlers begin acquiring new words at breakneck speed, a phenomenon known as the naming explosion. "They go from learning one to two new words per week to learning as many as nine new words a day," says Kathy Hirsh-Pasek, Ph.D., a professor of psychology at Temple University, in Philadelphia, and coauthor of How Babies Talk: The Magic and Mystery of Language in the First Three Years of Life (Dutton, 1999).
Some experts think that the naming explosion occurs once children discover that if their cup has a name and their daddy has a name, then everything else must have a name too. "Once they make that realization, they want to find out the names of everything around them, so they'll frequently ask 'Whaddat?' " says Dr. Hirsh-Pasek.
Next, children begin to form partial sentences, such as "Me eat!" At this point, they may understand simple grammar, even though they don't follow these rules in their speech.