To help preschoolers build their vocabularies, use new and interesting words in natural conversations. Try this at mealtimes or when presenting a new toy or material. Introducing a new word in context helps children learn what it means. For example, it’s easier for children to learn what a ukulele is when they can see and hear it as well as listening to you say the word.
From The Word Gap: The Early Years Make the Difference by Laura J. Colker