Why had they not brought Charles Wallace with them?

In "A Wrinkle in Time" by Madeleine L'Engle, Meg and her brother, Charles Wallace, are initially separated due to concerns about his safety and the challenges they face on their journey through time and space. Their mother believes that Charles Wallace's unique abilities make him vulnerable to the dangers they encounter. Additionally, Meg feels a strong sense of responsibility to protect him, which influences their decision to leave him behind. Ultimately, his absence creates tension and highlights the bond between the siblings throughout their adventure.