Young children, including preschoolers and kindergartners, have a great capacity to learn new words, and those words can be pretty sophisticated.
I read a lot of books to my daughter, obviously, and it’s clear to me that she learns a tremendous amount of vocabulary that way.
For example, a few days ago we were driving in the car and she said “Dad, I just saw a squirrel!” (we don’t have a lot of squirrels where we live, so it was eventful for her to see one). When I asked her what it was doing, she said “It scurried up the wall”. Not climbed. Scurried. That’s pretty sophisticated for a four year-old (I think) but really not surprising if you consider that she’s been exposed to this word multiple times and knows how to use the word appropriately. I think she learned it from multiple readings of whichever book of ours contains that word (she could probably recall which book it’s in, and it’s that kind of youthful memory that probably in part helps kids learn new words so easily).
I think a lot of parents and teachers have a tendency to dumb down (for lack of a better word) the vocabulary they use with young children. But since kids are capable of learning richer language, it’s a pity to do that.
I believe reading a lot of books, and reading them repeatedly, to my daughter enables her to reach higher levels of verbal expressiveness. When there’s a new word in a book, I explain to her what it means, and she seems to retain that information quite easily. That not only enriches her communication skills but also builds her confidence and self-esteem since she feels good about mastering more vocabulary.
I also make it a point to introduce new words to my daughter in my own conversations with her that are related to the matter we are discussing so she can grasp the meaning easily.
So, parents and teachers, do not hesitate to read lots of books with rich vocabulary and use lots of sophisticated words with your children. Their capacity to handle “fancy” words will surprise and delight you.