Just buying a book and sitting it on a shelf isn’t going to do a thing. What’s important is the interaction between you and your child as you read to him/her every day. Your child learns that reading and discussion are so important that the most essential and significant person in their lives takes time to sit down and do it with them.
Babies start out really early comparing things. For instance, very soon they know the difference between mom and dad and the rest of the people in their environment. They show this by what they do when Mom and Dad come into their view.
When children connect books to their actual experiences, they have the opportunity to think about what they know already; what the book shows, and come up with their own questions and own ideas
Children are learning a LOT, incidentally, as they are following a parent around. Helping your preschooler learn the alphabet can be incidental to normal daily activities. Make it lighthearted and fun.