Popular series for kids reading on the third grade level or blue dot are:
Jigsaw Jones
Stanley
Junie B. Jones
Ivy + Bean
Nancy Drew and the Clue Crew
Judy Moody
Puppy Place
Horrible Harry
Cam Jansen
Magic Tree House
Boxcar Children
Geronimo Stilton
Baily School Kids
A-Z Mysteries
Weirder School
Note: This is a generalized list and levels may vary.
If you have others that you would like for me to list, I would appreciate all input.