The online retail giant first detailed its children’s book subscription service in early May, when it was only available to a select group of people.

Users must choose whether they want a box of children’s books to be delivered every one, two, or three months. Each box of kids books will cost $22.99, Amazon said.

Unlike Amazon’s (AMZN) other retail services that use algorithms to determine what interests its users, the Prime Box service relies on human “Amazon Books editors” to curate the selection.

“Our Editors read thousands of books every year to find selections your reader will enjoy again and again,” the company said on a description page for its service. “You’ll discover new releases, classics, and hidden gems tailored to your reader’s age.”

Parents will have to tell Amazon how old their children are so the company can tailor its choices based on age.

Children 2 years old and younger will receive a box of four “board books,” while those who are older will receive two hardcover books determined to appeal and be relevant to their age groups.

Amazon said that while its staff will determine the books, people will be able to “preview and tailor the books from a list of curated options, or let the books be a surprise.”

The service is a logical step for Amazon, which became a technology giant by initially selling books online. Additionally, the company’s Prime subscription service has become increasingly important in its overall strategy to expand into new areas like video streaming and other services.

Get Data Sheet, Fortune’s technology newsletter.

In April, Amazon CEO Jeff Bezos said Amazon Prime has more than 100 million subscribers worldwide, but didn’t say how much revenue the service makes.