I saw this film short twice around 1980 or 1981. Once was in a theater before a matinee of who-knows-what. The second time was on HBO’s “Short Takes” that they used to show between movies.
It starts with a young boy riding his bicycle and singing a song. He arrives at home to find his older brother mixing up some concoction in the kitchen.
The two go out to play in their yard for a few minutes, then go back into the house. The older boy makes his younger brother drink the potion, and he turns into a chicken, but still has a young boy’s voice.
The chicken boy then threatens to tell their mom, so the older boy adds one or two more ingredients and has the chicken drink it, and he changes back into his brother.
Does anyone remember this, or better yet, its title?