Why won't Mrs. Murry be worried about Meg and Charles Wallace?

Mrs. Murray won't worry about meg and Charles Wallace because Mrs. Whatsit has fixed it so that she sill not even know they're gone.

"Now, dont worry, my pet," Mrs. Whatsit said cheerfully. "We took care of that before we left. Your mother has had enough to worry her with you and Charles to cope with, and not knowing about your father, without our adding to her anxieties. We took a time wrinkle as well as a space wrinkle. It's very easy to do if you just know how."