The Boxcar Children #1 by Gertrude Chandler Warner
"Henry, Jessie, Violet, and Benny, four orphaned brothers and sisters, suddenly appear in a small town. No one knows who these young wanderers are or where they have come from. Frightened to live with a grandfather they have never met, the children make a home for themselves in an abandoned red boxcar they discover in the woods. Henry, the oldest, goes to town to earn money and buy food and supplies. Ambitious and resourceful, the plucky children make a happy life for themselves—until Violet gets too sick for her brothers and sister to care for her."—Summary
Dinosaurs Before Dark (Magic Treehouse #1) by Mary Pope Osborne
"Where did the tree house come from?
Before Jack and Annie can find out, the mysterious tree house whisks them to the prehistoric past. Now they have to figure out how to get home. Can they do it before dark, or will they become a dinosaur's dinner?"—Summary
The School is Alive! (Eerie Elementary #1) by Jack Chabert
"Sam Graves discovers that his elementary school is alive and plotting against the students. As Hall Monitor, it is his job to protect them—but he will need some help from his friends."—Summary