How and why does Calvin fit in with the Murry family?
Calvin is similar to the Murrys in that he looks at life unconventionally. They meet when Meg and Charles Wallace run into him near the "haunted" house where Mrs. Whatsit, Mrs. Which and Mrs. Who live. Calvin explains that he felt a "compulsion" to visit the haunted house and mentions often having such compulsions. In other words, like Charles Wallace, Calvin listens to his intuitions. Although he is popular at school, a good student and a basketball player, he doesn't feel anymore at home in this conventional environment than do Meg or Charles Wallace. He explains to Meg that while he fits in superficially, the everyday high school world really isn't for him. Until the Murrays, he hasn't met anyone who truly understands him and who he can talk to about subjects that matter. As he puts it after meeting the Murrays, "I feel as though I were just being born! I'm not alone anymore!"
Like Mr. Murry, Calvin is tall, thin and blue-eyed. Like the Murrys, he's caring, he's open to new ideas and he has had pain in his domestic life. If the Murry father has disappeared without a trace, Calvin suffers because his mother, with eleven children, is overwhelmed and unable to adequately care for her family. Calvin has so much in common with the Murrys in terms of outlook, and they fill such a gap in his home life, that he clicks almost instantly with his new "family."
The reason why and how Calvin fits in with the Murry family is because he isnt exactly a normal person just like Charles Wallace, they both have something in common. He almost has the behaviors and personalities as Meg and Charles Wallace. It almost seems like he is a part of the family