The Guardian (1990)

Phil and Kate have a baby boy named Jake. They hire a baby-sitter, Camilla, to look after Jake and she becomes part of the family. The Sterling's friend and neighbor, Ned, takes a liking to Camilla and asks her out. She refuses, but Ned follows her and discovers that she is not quite human. Camilla discovers that she has been followed and Ned is pursued. He leaves a desperate message for Phil and Kate which reveals that Camilla has special plans for baby Jake.