Overextending is when instead of relying on an adult to tell them a word, your toddler sorts the information they know and tries to find a word that best matches. For example, they will usually categorise objects according to their size, colour, shape, movement sound or texture.[1]
They know a dog is a dog, and when they see other four-legged animals, they call them all dogs. The same is true when they see a man and call them, “Daddy.”
They are using their knowledge of the world and linking the similarities they see but their understanding is too general and they haven’t learned all the words they need to know.[2]
When a toddler underextends a word, they don’t use the word for enough objects or animals.
In the case of a dog, your toddler might know that they have a pet dog, and it is theirs. As their vocabulary is limited, they are unaware that the term "dog" might refer to dogs living in other households. Their understanding of the word ‘dog’ is too narrow.[2]
So, if they see a dog in the park, they won’t assign a word to it. When told it is a dog, they will likely disagree. They might become frustrated because their understanding of the word dog explicitly refers to their dog at home. They do not understand that a dog is a dog; dog is the name for their dog and nothing else can be called the same name.
Another example could be when they ask for a drink. Your toddler may associate their own cup with having a drink. So, if you pour the drink into a different cup, they don’t see that as their drink.
Again, your toddler is using life experiences to fill a gap in their language. They seek the best, most accurate word they know to get their meaning across.
Both over and underextending words are a normal stage of development.
Your toddler’s language skills are developing quickly, and they are trying to use the best language they can to describe what they mean. Bear with them as they navigate their way through learning and understanding word meanings.
You can support your toddler by helping them understand the meanings of over and under extended words. When you hear a word being used too narrowly or broadly, discuss the word and the many ways to use it.
References:
[1] Saxton, M. (2017) Child Language Acquisition and Development, 2nd Edition. Sage Publications Ltd.
[2] Wałaszewska, E. (2011) Broadening and narrowing in lexical development: How relevance theory can account for children's overextensions and underextensions. Journal of Pragmatics.