Moonbird
Moonbird is a 1959 short animated film by John Hubley and Faith Hubley in which two boys have an adventure in the middle of the night as they sneak out and try to catch a 'Moonbird' and bring it home. The film was animated by Robert Cannon and Ed Smith. It won an Academy Award for Short Subjects (Cartoons) in 1959.
Moonbird featured the voices of the Hubley's sons, Mark and Ray ("Hampy"). For the Moonbird, the Hubleys secretly recorded the boys sharing an imaginary adventure before going to sleep in the darkness of their room. Their parents afterwards took the tapes and created an animated film to fit their sons' story.
The cartoon shows the little boys climbing out their bedroom window and going on a quest for the Moonbird, trying to trap the Moonbird, and otherwise obsessed with the Moonbird which they never do encounter, though we see it following them about from place to place, leaping in and out of their trap, and in general keeping an eye on them.[1]
The film has lapsed into the public domain and can be found on numerous discount cartoon compilations.