Why does raymond think that children like scout and dill can understand his secret better than adults?

Mr. Raymond thinks this, because Scout and Dill have not yet been alive long enough to become corrupted and hateful. The adults in Maycomb have built up years of gossip and prejudices, but Raymond sees young children such as Scout and Dill as a type of clean slate, who can still be educated about the way others live, and can understand things differently than the others in town.