The Brood
(1979)

An early Cronenberg film inspired by a custody battle for his daughter.

A psychotherapist Dr. Hal Raglan (Oliver Reed) uses "psychoplasmics" which allows negative emotions to cause a patients body to undergo physical change. For his patient Nola Carveth (Samantha Eggar), the result is parthenogenetic reproduction (insect like reproduction where unfertilized eggs develop into lifeforms) creating mutant children who have a telepathic bond with their mother. Whenever mommy is upset, the mutants go on a rampage.

Nola is divorced from Frank Carveth (Art Hindle) and is completely isolated at Somafree clinic where she is being treated. Frank refuses to bring their daughter Candice (Cindy Hinds) to see her mother on weekends since he noticed that she had been beaten. Acting on their "mothers" emotions, the mutant children kill Franks' parents, Candice's school teacher and kidnap Candice.

Frank goes to Somafree where Frank and Dr. Raglan decide that Frank will keep Nola distracted while Dr. Raglan rescues Candice from the mutants. Things are going okay until Nola reveals to Frank what she is by birthing a mutant in front of him. All hell breaks loose and Dr Raglan is killed after wasting a number of mutants. Candice is trapped behind a door with mutants trying to break in to get her. Frank freaks out and kills Nola, causing the mutants to die. Frank takes Candice away but we see that Candice is developing a pustule which means she is going to be just like her mother and spawn more mutants.   

Thanks Don P!