Introducing sign language to your child can increase their word exposure and vocabulary. When you teach them signs you typically repeat words more often, which may expand your child’s receptive and expressive vocabulary.
For example, when I give my son his milk I will hold the milk, sign milk, and say, “Do you want your milk?” Then he usually smiles and I continue with, “Theo wants his milk,” while signing milk again. Then while I feed him I continue saying the word milk, paired with the sign. When you are trying to teach your child a sign you repeat words more than if you were not teaching them signs. Another example is during mealtimes, I will say, “Does Theo want to eat (sign the word for eat) his apples (sign apples)?” Then during the whole 20 minutes it usually takes to feed him I repeatedly say and sign eat and apples. If I were not teaching him signs I would not feel as obligated to say (and sign) eat and apples before every bite.
When I began signing to Theo, I found myself talking about items more and repeating myself more. This repetition leads to increased word exposure and has the potential to expand his vocabulary.
Also, teaching your child signs can lead to more elaborate thought processes¹. For example, if your child has a store of signs they know and use, you can ask them, “What do you want to eat?” instead of asking them if they want a specific thing like “Do you want apples?” By posing the first question you are giving them the opportunity to think about their options and choose (with a sign), which entails a more elaborate thought process compared to the yes or no question of, “Do you want squash?”
“Signing babies tend to have larger vocabularies once they start talking because they’ve been able to use more advanced language and are often asked more elaborate questions because their comprehension is clear to the parent.” – Laura Berg
With our preverbal children, we often do not know what they are comprehending so we keep our language simple¹. But when a child signs they are showing you what they comprehend so we tend to introduce more vocabulary to them. For example, if you start teaching your child the signs for milk, eat, and more at 6 months and they start signing back at 8 months you then teach them more signs. Now you add the words all done, bath, and bedtime to their repertoire because you know they comprehend milk, eat, and more so you can introduce more. Once a child’s comprehension is evident to the parents they tend to use more advanced sentences and ask more elaborate questions, leading the child to use more elaborate thought processes.