It's the Great Pumpkin, Charlie Brown (1966)

Charlie Brown is excited to be invited to Violet's Halloween party--his first-ever party. Before the party, the Peanuts gang plans to go trick-or-treating; meanwhile, Snoopy, dressed as the WWI flying ace, takes his Halloween persona to extremes. Linus won't be joining them for trick-or-treating or the party: he will be waiting in the local pumpkin patch for the arrival of the Great Pumpkin. Linus believes that the Great Pumpkin rises out of the most sincere pumpkin patch--one more sincere than his own local one--flies into the air, and delivers presents to all the boys and girls around the world. Because of his belief, Linus is the laughingstock among his friends. Sally is torn between going trick-or-treating for the first time and attending Violet's sure-fire fun Halloween party, or following her love Linus and waiting for the Great Pumpkin's arrival with him.