Overextension: When children apply verbal labels too broadly. For instance, calling all four-legged animals 'dog'.
Underextension: When children apply verbal labels too narrowly. For instance, using 'dog' only for their pet dog and not recognizing other dogs as 'dogs'.
Telegraphic Speech: This refers to two-word sentences commonly used by toddlers where non-essential words are omitted; e.g., "want juice."