Gregory the Overlander by Suzanne Collins (and sequels). Chapter Book.

“When his two-year-old sister Boots tumbles into an air duct in his building’s laundry room, Gregor leaps after her and they fall, à la Alice, into another world. Gregor wants desperately to get home—until he hears that his father, who left Gregor heavy-hearted by disappearing two years ago, may be in Underland himself, kept prisoner by enormous, war-hungry rats… (Fiction. 8-12)” Source: Kirkus Reviews

Recognize the author name? Collins wrote the blockbuster series The Hunger Games.

This is another good read-aloud for multiple ages. Boots injects light hearted comedy into this sometime dark tale.