The website TheFW.com has put together a list of "Things You Didn't Know About 'It's the Great Pumpkin, Charlie Brown'":
Here are a few highlights:
The Original "Great Pumpkin" Story Was Actually About Religion . . . Apparently, when CHARLES M. SCHULZ created the Great Pumpkin for the "Peanuts" comic strip, he was actually using it to show how SACRILEGIOUS it was to believe in Santa Claus.
Kids Sent Candy to Charlie Brown After It Aired . . . The director has said that some kids felt so bad about Charlie Brown only getting rocks while trick-or-treating that they actually mailed candy and other gifts to CBS addressed to Charlie Brown.
The First Adult to Record a Voice for a "Peanuts" Special Was for Snoopy . . . The director provided the voice for Snoopy in "Great Pumpkin", a role he continued in the later specials. It was the first time an adult voiced a "Peanuts" character.
Lucy Is Reading a "TV Guide" Featuring Herself on the Cover . . . Here's something you may not have noticed: Early in the movie, Lucy is briefly shown reading a "TV Guide" . . . that has a picture of HERSELF on the cover. It happens after Linus writes his letter to the Great Pumpkin . . . and he walks past her on his way to the mailbox.