Young children develop all sorts of motor skills as they grow. Here are some that pertain to books and literacy.
At 6-12 months a baby can reach for a book, and put it in his mouth. He can sit in your lap, hold his head steady and turn pages with adult help.
At 12-16 months a baby can sit without support, may carry a book, can hold a book with help, and turn pages of a board book, several at a time.
At 18-24 months, a baby can turn pages of a board book, one page at a time, and can carry a book around the house.
At 24-36 months, a toddler learns to handle paper pages, and goes back and forth in books to find her favorite pictures.
At ages 3 years and up, a child exhibits competent book handling and can turn paper pages, one page at a time.