It's 1934 and Margaret Mildred Kittredge, a.k.a. Kit (ABIGAIL BRESLIN), is a 10-year-old girl who dreams of being a reporter for her hometown paper, the Cincinnati Register, when not inducting new kids into her tree house club along with fellow member Ruthie Smithens (MADISON DAVENPORT). Unlike Ruthie's dad who runs the local bank and is foreclosing various homeowners, Kit's father (CHRIS O'DONNELL) is having problems making ends meet at his car dealership.
Nonetheless, Kit's mom (JULIA ORMOND) always tries to look on the bright side of things, even when Uncle Hendrick (KENNETH WELSH) thinks the family is living beyond their means. Of course, they're doing better than many, including young hobos Will Shepherd (MAX THIERIOT) and Countee (WILLOW SMITH) who offer to work in exchange for food, an agreement that doesn't sit well with snooty snob Louise Howard (GLENNE HEADLY).
When Kit's dad loses his job, he ends up moving to Chicago to look for work, while her mom has no choice but to take in boarders, including Louise and her young son Stirling (ZACH MILLS) who defends Kit from verbal taunts coming from Roger (AUSTIN MACDONALD), the class bully. Other boarders include mobile librarian Miss Bond (JOAN CUSACK); dance instructor Miss Dooley (JANE KRAKOWSKI), magician Jefferson J. Berk (STANLEY TUCCI) and later his brother, Freidreich (DYLAN SMITH).
While that somewhat extends her "family," Kit is worried that she and her mom will end up having to sell eggs, an act the girl sees as meaning one's hit rock bottom. Accordingly, she tries to pitch her stories to the local paper's city editor, Mr. Gibson (WALLACE SHAWN), especially when she learns she can get paid for any that are published.
With public sentiment toward the hobos, including Will and Countee who live in a "hobo jungle" with the likes of Shelton Pennington (COLIN MOCHRIE) and many others, Kit decides to focus on their story. Yet, when crimes start occurring and the hobos are fingered as the culprits, Kit tries to get to the bottom of the issue, all while hoping that her dad will soon come home.