Csutak and the Grey Horse (1961)

Csutak is just a pain in the neck, the little boy is even excluded from play by his mates. Vacation is spent lonely until one day he sneaks the woman haulier's old, shabby horse, a creature that would be better off in a slaughterhouse, out with himself. Possessing the animal is the key to the children's gang. They all try to find a place for the horse.