Cupcake Diaries (10 book series) (10-12 years) by Coco Simon

This first book in The Cupcake Diaries is told through the perspective of Katie Brown. We find Katie miserable on the first day of middle school. Her best friend Callie came back from camp boy-crazy and part of a whole new group of friends. When it’s made clear that Callie is in the PGC (Popular Girls Club) and Katie is not invited to join, Katie suddenly feels incredibly alone. Katie realizes if she’s going to survive middle school she needs to seriously regroup and find some new friends. But how? She bites into the cupcake her mother packed her for lunch and for a second closes her eyes. The sweet treat makes her happy—finally something goes right! Looking around her table, Katie notices the other students seeming a bit lost, as well. Which gives her an idea…With three new friends Katie forms a club as a way to spread the cupcake love and earn some cupcake cash.