I came across this article in Science News while I was restocking our library's magazine display! In 2-year-olds Possess Grammatical Insights, Bruce Bower writes, "Budding toddlers recognize the difference between nouns and verbs in simple sentences, even though the kids don’t utter such sentences for at least another year."
When researchers measure the electrical activity in a toddler's brain, they show a marked increase in activity when the toddlers hear sentences in which the nouns and verbs have been used in the wrong place. This shows that toddlers already have an understanding of what is the "right" placement for those types of words.
When we read or talk to young children, we are giving them the examples they need to help their language centers develop!