So many great suggestions given already, brings back so many childhood memories. I loved the Nancy Drew and Bobbsey Twins series. I also read all the Choose your own Adventure series and anyone else remember Encyclopedia Brown?
Since this lockdown started, I discovered that my public library has an extensive digital collection that can be accessed on cloudLibrary. Tons of new titles, children and teen books, even current issues of popular magazines. All you need to have is a library card number, but if you don’t, I would think they can take requests for new library cards via email, mine does.