Why is mother upset

After a hearty dinner, Calvin goes upstairs with Charles Wallace and reads him the book of Genesis as a bed time story. Meg continues doing her homework, but has trouble concentrating and begins to ask her mother why she is upset. They discuss Charles Wallace and how he is different from other people, though Mrs. Murry can’t explain just how. Though he doesn’t look any different from other people, she tells Meg, he has a different essence, something that makes him different inside. Calvin returns from reading to Charles Wallace and he and Meg decide to go for a walk.

here's another;

Mrs. Wallace is upset by Mrs. Whatsit's parting remark about a tesseract.