The language in books is not the same as the language of conversation. In books, sentences are more complex and vocabulary is more sophisticated. Adults can help young children understand book language by choosing books on topics that are already familiar. If children have experienced and talked about something, then a book that is related to the experience is a good choice to read aloud. For babies this means reading books about pacifiers, diapering and bathtime. The wider a child's experiences, the more topics they are capable of learning about in books. New language gets mapped onto concepts that the child has already mastered.
Tumble Books | Homework Help
Center for Early Literacy Learning
Too Small to Fail
Reading is Fundamental
Helping Children Read and Succeed
Ohio Department of Education
PBS Kids | Sprout