Ringing Bell (1978) is arguably one of the most disturbing children's films of all time.
This was an incredibly depressing 47-minute film from the 1970s, released by Sanrio--best known for Hello Kitty--under the name
Chirin no Suzu. It was dubbed and released here on VHS in 1983, completely intact and with nothing done to hide that it was a Japanese cartoon (except for the fact that the bad wolf Wor was re-named the "Wolf King" in the US dub). However, it's been out of print for decades and there's no DVD (at least, not in America).
In this sordid tale, Chirin the lamb is orphaned when the bad wolf Wor kills his mother. Chirin sets out for revenge, but has a change of heart. Despairing of his weak nature, he begs the wolf to teach him how to be tough, and learns how to be a predator from his parent's killer.
Battered, bruised, and half drowned, the lamb is put through a heartless regime of torment, until he is toughened into a vicious ram with a "reputation for ruthless killing".
Two years later, Chirin is led by Wor in an attack on the farm where he was born. Seeing an ewe vainly fighting to protect her offspring, Chirin is reminded of his mother, and turns on the wolf – killing his surrogate father. However, the rest of the flock is afraid of Chirin, and he remains an outcast, forced now to wander the savage world without any companionship at all. Chirin is "never seen again", though it is said that sometimes the sheep hear the distant tinkle of the bell around his neck.
Great fun for the whole family.