When a Sound Becomes a Word
The shift from babbling to real words is a gradual process that takes place in a series of steps. First, many babies invent protowords -- made-up words linking sound to meaning, like saying "muhmuhmuh" to indicate that they want to be picked up.
They begin to use words imprecisely at about 1 year, using a word only in one context or too broadly. For example, when he was 15 months old, Joshua called his rubber toy "frog" but never used the word when he saw a frog in a picture.