Now that we're getting a Harry Potter sequel, there are plenty of other book series we wouldn't mind seeing make a comeback, either.

Potter fans rejoiced in October when news broke that a sequel to the incredibly popular franchise is on the horizon by way of a new play, Harry Potter and the Cursed Child. Featuring a cast of over 30 actors, the show will tell the eighth story of the Harry Potter series and jump 19 years into the future from where book seven, Harry Potter and the Deathly Hallows, left off. It will premiere at the Palace Theatre in London's West End in 2016.

Fans of the Fifty Shades series have been rewarded with new material as well. In June, author E.L. James released Grey, a retelling of the book's original story through the perspective of its male protagonist, Christian. More than a million copies of the title were sold in just four days.

Of course, films have been doing sequels and reboots for years, and the trend has caught on in television, too. A number of old favorites have come back to life as of late. Gilmore Girls is reportedly in talks for revival via Netflix, and The Muppets, The X-Files and Full House are on the air or back in production already.

If what's old is new again in film and television, why can't it be in the book world, too? Here are seven series we would love to see come back to the shelves -- even if most of them are for kids (adults like kids books, too!).

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1. The Baby-Sitters Club

The Baby-Sitters Club series made Kristy, Claudia, Mary Anne and Stacey every '90s girl's best friends. Running from 1986 through 2000, the series included 213 titles, with the publisher printing 176 million copies of the books.

The series followed the adventures, friendships and mishaps of a group of middle school girls living in Stoneybrook, Conn., who start their own babysitting business, the baby-sitters club. Ann M. Martin, the series' creator, wrote more than 60 of the titles; other authors ghostwrote some of the books. The Baby-Sitters Club spurred a number of spin-off books as well as a television series and a movie by the same title released in 1995.

The series made a bit of a comeback in 2009 when publisher Scholastic announced plans to reissue repackaged and slightly revised versions of The Baby-Sitters Club series and publish a newly-written prequel, The Summer Before, which came out in 2010. Nothing new has been released since.

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2. Sweet Valley High

Before we had Taylor Swift's "squad," we had the ladies of Sweet Valley High.

The books follow California high schoolers and identical twins Jessica and Elizabeth Wakefield along with their friends Enid Rollins, Lila Fowler and Maria Slater. Created by Francine Pascale, the series began in 1983, resulted in the publishing of over 150 titles, and has taken on various iterations, including a board game.

Pascale last rebooted the series in 2012 with a six-part e-serial on the Wakefield sisters at age 30, The Sweet Life.

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3. The Wheel of Time

Fantasy series The Wheel of Time was originally planned as a six-book endeavor. It eventually turned into 14 volumes, with a prequel and companion book in the mix as well. And a handful of the titles were published after the author's death.

The Wheel of Time conceives a universe built by the Creator, who also forges the wheel of time, which has seven spokes representing a different era. The Creator imprisons its antithesis, the Dark One, who manages to escape and bring his influence back into the world. The series depicts a complex, magical world that takes place across the ages in both the past and the future.

James Oliver Rigney Jr. published the first title in the series in 1990 under the pen name Robert Jordan. He passed away in 2007, before completing what was expected to be the 12th and final volume of the series. Luckily, he left behind enough notes for fellow fantasy author Brandon Sanderson to complete his work.

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4. Animorphs

The Animorphs books came fast and furious, with 54 titles published from 1996 to 2001. They also spurned a television series, a line of toys, and a set of four companion books, Megamorphs.

The series revolves around a group of human teenagers and one alien who have the power of shapeshifting and turning into any animal they touch. They battle a secret infiltration of the earth and fight against a takeover by a group of aliens called Yeerks.

All of the Animorphs novels were published under the name K.A. Applegate, though many of them were penned by ghostwriters. The series is considered to be among the most successful children's book series of all time, alongside franchises like Harry Potter and Goosebumps.

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5. Bobbsey Twins

The Bobbsey Twins has been around for more than a century, with the first title in the series published in 1904. Across more than seven decades through 1979, 72 books were published, and an additional series of 30 titles were released from 1987 to 1992.

All of the books were penned under the name Laura Lee Hope, but the identity of the series' true authors has been a subject of speculation for years. The concept was created by Edward Stratemeyer, who is believed to have penned at least the first title before hiring ghost writers to complete the rest.

The series follows the adventures of the children of the upper-middle-class Bobbsey family, which includes two sets of fraternal twins.

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6. Encyclopedia Brown

Encyclopedia Brown follows the adventures of Leroy "Encyclopedia" Brown, a boy detective with a knack for trivia. He solves mysteries through his own detective agency in the fictional town of Idaville, ME.

The first book of the series, Encyclopedia Brown, Boy Detective, was published in 1963 and written by Don J. Sobol, who wrote or co-wrote all of the 28 novels produced in the series. The final title, Encyclopedia Brown and the Case of the Soccer Scheme, was published in 2012, just a few months after Sobol's death.

It was reported that an Encyclopedia Brown movie might be in the works in 2013.

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The Hardy Boys

Another Stratemeyer creation, The Hardy Boys first appeared in 1927. Published under the pseudonym Franklin W. Dixon, the books follow teenage brothers and amateur detectives Frank and Joe Hardy. The series has undergone several reincarnations over the years, the latest being The Hardy Boys: Undercover Brothers. The last title under that reboot has was published in 2012.

Nancy Drew, another mystery-themed franchise developed by Stratemeyer just a few years after The Hardy Boys, is actually still around. Today, readers can catch up with girl sleuth Nancy Drew in the Nancy Drew Diaries. The most recent novel was released in September 2015.

This article is commentary by an independent contributor. At the time of publication, the author held no positions in the stocks mentioned.