Hello Sara! Thanks so much for your kind words and visiting my website. You certainly have really strong readers for second grade! THey will thrive with book clubs! For your J/K readers, I would offer a few different choices (depending on availability) of beginning chapter books that they can choose from. For example, you could check out a multiple copy books of the following, which are at a J/K level:
Any books in these series: Henry and Mudge, Mr. Putty and Tabby, Amber Brown, Young Cam Jansen Mysteries, Poppleton, Arthur.
I hope this helps! Best of luck to you…as I will be implementing book clubs with my second graders right now, too! Be sure to follow me on Instagram :)