"The Box-Car Children" by Gertrude Chandler Warner is a children's novel originally published in 1924. Four orphaned siblings—Henry, Jessie, Violet, and Benny Alden—flee from a baker who would separate them and discover an abandoned boxcar in the forest. They transform it into their secret home, determined to stay together and avoid their grandfather, whom they believe to be cruel. Through resourcefulness and devotion to each other, the children create a new life, unaware that their fears about family may be unfounded.
Wikipedia page about this book: en.wikipedia.org/wiki/The_Boxcar_Children