1955: Peanuts Halloween

It's hard to believe, but at this point in the mid-1950s, Charles Schulz was one of the only ones celebrating Halloween in comics!

1952: Peanuts Halloween and Linus' first appearance

If there was a Great Pumpkin in 1952, Linus couldn't have known it yet.  His first appearance in "Peanuts" was in the September 19, 1952, strip, when Lucy announced to Charlie Brown that her baby brother could sit up all by himself.  Kind of.

Here we have another reference to Charlie Brown's head looking like a pumpkin.