Film about a psycho babysitter......?

Am trying to find out what film it was where there was a babysitter who lived in a house across a lake. Possibly late 70's to early 80's. Could be 'made for T.V'. She murdered all the family and wrapped them in plastic and sat them on the sofa. A line I remember from the movie is when the phone is ringing. She shouts 'I'll get it', even though all the family are dead..