Why does Mama take the children to visit Mr. Berry instead of scolding or whipping them?

Mama wants the children to see Mr. Berry for themselves, to understand the dangers and results of racist acts, to make them understand the world around them. It is one thing to "hear" something, and a completely different thing to "see" it. Scolding and whipping them would be a punishment, but actually seeing Mr. Berry is a life lesson.