Charles Schulz initially experimented with including adults in the Peanuts comic strip during its early years, but later abandoned the idea entirely, calling it "something I never should have done." Beginning in May 1954, strips briefly featured adult figures, legs and hands, but Schulz ultimately recognised that adults did not belong in his creation. This decision became one of the most unusual and important rules of the strip, fundamentally shaping its identity.

Schulz believed that the presence of adults would intrude upon a world that worked precisely because it belonged exclusively to children. By keeping the characters isolated from the grown-up realm, he allowed them to discuss philosophy, worry about rejection and contemplate life's disappointments without adult explanation or intervention, making their problems both funny and profoundly meaningful simultaneously. He eventually eliminated all visible adults and even unseen adult voices, instead keeping the grown-up world entirely off the page—allowing characters to be discussed and parents to be mentioned without ever appearing in the frame.