The Dwarf Sorcerer (1974)

Original title: Yi cun fa shi

After seeing his father murdered and his mother abducted by a caveman-like martial arts cult, a small boy is taken in by a wizened old kung fu master, who rigorously trains him until he is endowed with almost supernatural fighting skills. This training, however, takes much less time than it would in most martial arts films, in which the kid would attain mastery at about the same time he reaches adulthood. Instead what we get is a sword-wielding 5 year old waging a bloody war of revenge against an assortment of adult-sized demons and people in heartbreakingly threadbare monster costumes.