If you think that J. K. Rowling will be returning to Hogwarts on her next book for children, then you'll be disappointed. She's not closing the door on writing something new about our favorite magical world, but she's not going to venture into that direction anytime soon. When asked about a possibility of writing a prequel, most especially on the Marauders:
Rowling, speaking at the Independent Bath Literature Festival last night, said she was not planning to return to the story of the "Marauders" – who attended her fictional Hogwarts School of Witchcraft before Harry Potter – because she didn't think much of prequels. "I'm never going to say never but I have no current plans. I think prequels are not generally very successful," she said.
An article in Hypable also revealed that "her next book will be aimed at 8-year-olds, but she’s still busy writing it."
Supplementing this revelation was a quote from Independent:
Rowling referred to the children's book she was writing but refused to reveal much more other than that it might be for a younger age group than the Potter series: "It will be shorter. I'm very bad at estimating what sort of age group will like this... I think it might be for slightly younger children."
After she released The Casual Vacancy, I can never again read any J. K. Rowling book with innocence and every phrase would have a greenish innuendoes. I just hope after reading this new and upcoming book, even if it's for children, I could regain a clear mind once again...