I saw this movie when I was young about a girl who starts killing off her family one by one. I saw it on tv sometime in the mid to late 90s. The family in the movie seemed big to me (so at least 3 kids, mom and dad) and lived in a 2 story brick house with a tall tree close to the house. I remember that because she either kills or seriously injures one of the other kids by convincing them to climb on the roof to fetch a Frisbee or something, and of course the kid falls off. She gets the dad by somehow dropping a radio into the bathtub while he is in it and electrocutes him. I think the little girl killing people was blonde with a ponytail, between 11 and 13 years old? She may have been adopted, I’m not really sure. This has been driving me crazy since I was a kid.
Don’t Go To Sleep (1982)?
http://www.imdb.com/title/tt0083844/?ref_=fn_al_tt_1