I watched final part of movie/short/omnibus in 1990.It is made probably in middle of 80's.
The electricity in house is shut off.In further everything is acting in the dark house.
Chunky boy,about 10-12 years old,black haired,run away deep in house and ask
Mother to play with him,to find him(mother is brunett,about 40 years old).
Chandelier falled off,nearly hit woman.Somebody has phone-called(male voice),
Woman answered and says?? (name of boy)came back and knows everything.
She realized that person is repeating what she is talking.
She is asking:"Why are you repeating what I am talking" and the voice repeats
That final sentence,and laughs.
She realized that phone cable is actually disconnected.
Boy is tracking mother to the locked door-mother is hidden in some room.
Boy said:"Look what I found.A big and sharp knife.I hear you,you are upstairs,
but I will catch you!".Boy's voice departed and mother thinks he left,
It is safe for her to leave the room.She is leaving,but the boy is there with knife,attacking her and laughing.
She ran,hid in a car,he is attacking her.Than she running and hiding in room.She took a gun,
Boy accessed room,looking for her in the dark,attacking her,she shoot him
And he is falling through the window.
Epilogue:Woman left room,staing on stairs,exhausted.Boy breaks into the house.
Woman says?? (boy's name).He answered:
"I am not ??????.
????? sent us to kill you".And he is approaching her.Closing credits.

There are two movies with versions of this story:

Trilogy of Terror II (1996 TV movie)
From Wikipedia:STORY 2: BOBBY
It has been some time since Bobby drowned, leaving his mother, Alma (Lysette Anthony), depressed and guilty. While her husband is away on business, she determines to raise her son from the dead.. . Later, a thunderstorm approaches the beach mansion. Hearing a knock, she opens the door to discover her son. After cleaning him up, she begins to make him feel at home again. However, all doesn't work out when Bobby goes completely mad and begins to terrorize his mother in the dark house with a sledgehammer and a butcher knife. The mother soon realizes that it isn't Bobby who returned to her, but a demon which had taken his place...

https://en.wikipedia.org/wiki/Trilogy_of_Terror_II


Dead of Night (1977 TV movie)
The third segment is titled "Bobby".

Dead of Night (TV Movie 1977) - IMDb

Both TV movies are Dan Curtis productions. Curtis also produced both of the "Dark Shadows" series and "Kolchak: The Night Stalker". His "Trilogy of Terror" (1975 TV movie) spawned a sequel segment; the infamous native fetish doll who terrorizes Karen Black in the first film returns to hunt Lysette Anthony and museum guards in the second one.

Thank you.It's really professional answer.You know a lot about movies.
I watched that movie in 1990,so I search 25 years.I was looking for movie name
on 5 web sites and asked many people about this,but no answer till now.

Regards
Sasha

I never received this notification and am so pleased that I did answer your question! Yes, I always try to give as complete response as I possibly can.

It's very encouraging to me that you appreciate my effort.

I've been going over older answers, and I saw your reply. I wasn't ignoring you! I just hadn't seen this!