Amazon is expanding its Prime Book Box subscription service nationwide, delivering boxes of children's books at regular intervals to all its Prime members, the company announced Tuesday.

Members can choose to have the books delivered every one, two, or three months at $22.99 per box. Customers can select age ranges of 0-2 years, 3-5 years, 6-8 years, and 9-12 years.

Amazon says it has a team of book editors that "read thousands of books every year to find selections."

The service was initially rolled out in May by invitation only.