Mystery/ Fantasy book about some kids trapped in a Library that was burned down. Read 2019-2020. Spoiler.

[Mateja]

So I remember that I read this book 4-5 years ago
I remember it vaguely, I know that there are a group of friends trapped in an abandoned library that was burned down like 40-50 years prior. I think there was a creature or something haunting that library but im not entirely sure. THE MOST IMPORTANT PART THE LIBRARIANS KID WAS TRAPPED HERE FOR 40-50 YEARS AND WAS FOUND BY THESE KIDS AND THE LIBRARIAN AND HER KID REUNITED!!! thats the only part i remember vividly
Please if someone knows how this book is called please tell me i really need to know how this book is called thank you so so much🫶🏼

[Rainbowheart]

Are the characters ghosts?

Are they still children 40-50 years later, or adults?