What is the difference between underextension and overextension?

Underextension: this is a common semantic error made by children. it occurs when a word is given a narrower meaning that it has in adult language

e.g Only use the word dog for the family dog, not any other dog

Overextension: this is opposite of unserextension and is also a feature of child's early language. This occurs when a word is given a broader, more general meaning that it should have.

e.g.. calling another male "dad"
overextension occurs more frequently than unserextension and is the main semantic error made by young children.