[Hectocotylus]

In early 80s when I was a child I watched few minutes of black&white film on TV before my parents sent me to my bedroom, what I managed to see made huge impression on me. Please help me to find a title of that movie.
All I remember: there was a women with her two young daughters and they must have been some kind of aliens. In one scene there was sort of party, reception with many people sitting and eating at a big table, lot of food and even some musicians playing for the guests. These little girls had very weird toy, don't remember exactly how it looked like but it was small, they could keep it in the pocket. During that party naughty not-from-this-world-girls activated the toy and suddenly it became a massive monster attacking all the people around. What was strange - it was decapitating and throwing their heads around, some of the heads landed in the dishes and plates with food and were still talking and pulling faces! I also remember that people were in panic, screaming and running except of one blind old fiddler who kept sitting on a chair and playing his instrument. Nothing touched him. I think that woman had friend, a man (probably normal human from planet Earth), and as I remember they suddenly came. Seeing what was going on she immediately took the device, switched off and the monster disappeared...
I was perhaps 5 or 6 when accidentally watched this scene. I was equally impressed and confused! I would love to find this film now! Can anybody help me?