Have you heard of parentese?
Perhaps you don't know the term, but you're probably familiar with what parentese sounds like.
Here, in this entertaining 60-second spot from ParentingCounts.org, is a great example of parentese.
Parentese is a way of talking that helps Baby focus on our speech. Parentese often is characterized by speaking in a higher pitch, lengthening words and phrases, and putting added emphasis on certain words.
Here is one of the best articles I have read on the practice and use of parentese. It comes from the Center for Early Literacy Learning.