Question

When children use the word “doggie” to refer to every four-legged animal they see, __________ occurs. A. underextension B. overextension C. telegraphic speech D. overregularization

Answer 1

This is known as overextension! (the correct answer is B.)

this means that the children extend the meaning of the word to other words, but they also use it for more words than is correct (hence the "over-".
This is a very common phenomenon in the 2nd and 3rd year of life and is not considered dysfunctional.