I remember seeing this movie on TV in the “70’s. A teenage girl walks into her parents bedroom and sees them all slashed up on the bed and blood all over the room. I want to say that teenage girl was Cissy from Family Affair but I can’t find a movie like this on her Bio.
maybe Silent Night, Bloody Night (1972)?
http://www.imdb.com/title/tt0070694/?ref_=fn_al_tt_1
Could it be…Blood and Lace(1971)? The girl is played by Melody Patterson of F Troop fame, and sadly she passed away recently. Her parents are killed by a hammer right at the start of the movie which you can watch here: