The Cradle Will Rock (1992)*

Rebecca De Mornay is a nanny who it turns out is crazy and tries to kill Macauley Culkin. Or maybe it's just that Macaulay Culkin was in a similar movie around the same time.† I also sometimes get Rebecca De Mornay and Traci Lords confused. (Is this the movie with the literal cliffhanger at the end, or is it the one where an underage girl with a fake ID has unsimulated sex on camera for the masturbatory enjoyment of a country of perverts?)

Still from Black Throat (1985).

* IMPORTANT NOTE: I was thinking of The Hand That Rocks the Cradle.
† The Good Son (1993).