"A child of five would understand this. Send someone to fetch a child of five"

Groucho Marx's quote is an amusing way of stating that the subject at hand is so simple that even a child might comprehend it. He is recommending that the person he is talking to must not have any problem understanding the idea, and that if they do, they need to go and find a five-year-old to describe it to them. This quote is a humorous method of stressing how easy the concept is to understand. It is likewise a way of buffooning the person he is speaking to, indicating that they are not intelligent sufficient to understand the idea without the aid of a child. This quote is a humorous way of making a point and satirizing somebody in a lighthearted method.