It's Alive III: Island of the Alive (1987)

Director: Larry Cohen

Star: Michael Moriarty, Karen Black, Laurene Landon

Jarvis is in court defending  his "child" the right to live, but the court is questioning the safety of others until Jarvis proves that his "child" is safe.  The judge decides to place the "baby" on a desert island that the government owns.  There are already other babies there, so why not.  Jarvis travels there with doctors to release his child in the jungle to live free.  They get attacked by the other babies that have now grown up.  Jarvis escapes on one of the boats and lands in Miami.

At a shitty late 80's punk rock/new wave bar, whatever, you meet Jarvis wife, Ellen, played by the great Karen Black.  The couple had become famous because of their mutant child, so she left him and went into hiding.  She wants nothing to do with him or their child.

There was a boats left on Mutant Island, that's what I'm calling it, so the grown mutants show up on the shores of Miami.  They want to kill and find their parents.

This third installment was made 9 years after the second one, so it was an attempt to make a trilogy, but maybe they should have left the movies in the 70's where they belong.  It did give Karen Black some work though.

 It's Alive III: Island of the Alive (1987) Trailer