Why does Mrs. Murry think Meg and her brother Charles Wallace are smart?

Because Meg
and Charles Wallace are somewhat different from the rest of their small town, Meg is often made
to feel stupid, while Charles Wallace, who didn't speak until he was four, is also thought by
some of the townspeople to be slow. We as readers know early on that  the young Charles Wallace,
who speaks in full sentences, anticipates the needs of his mother and sister, and uses complex
vocabulary when he wants to, is intelligent, even if the community does not. However, Mrs. Murry
also has evidence that both children are smart because she and her husband have played games
with them that were in fact secretly IQ tests, and both children scored very well. Given the
later message in the novel about the severe problems with conformity on Camazotz, we can
understand Meg and Charles Wallace's tendency to be different as a valuable
trait.