Okay, this one is going to be packed with random info. I saw this movie on television in the early 90’s when I was 4-5 .
The movie was in English and it was in color.
I would say the movie is probably from somewhere in the early-to-mid 80’s.
A boy walks into a room and notices someone sleeping (or dead) and takes an item from them and walks out. He’s shown to be the stereotypical nerd with glasses and a tucked in, button up shirt. There were scenes of him putting on headphones and tinkering around with what seemed to be a giant computer or radio system.
In one class, a bully teases him and he makes a mixture in a beaker and pours it on the bully’s arm. Turns out it was acid.
Later on at home, the parents are going out and hire an older woman to babysit him and his sister. One scene has the woman pouring milk for her kitten and puts a box over it as its drinking, but later when she lifts up the box, the kitten is gone. I think the boy appears holding and petting it before her.
The boy is shown in either the front yard or backyard, setting up a light sensor system. The bully shows up later, now with a bandaged hand and crosses the sensor, alerting the boy. I think they end up in the garage when the boy shows up with a sword and spiked helmet. A piece of wood or cardboard falls when they scuffle and the bully tries to push it forward but the boy stabs the sword through, killing the bully.
Don’t remember how it starts, but the boy and the babysitter fights and he ends up throwing her kitten into the fire. When she’s crying over it, he knocks her out (i think). As she’s on the ground, he gloats and pours alcohol/wine on her face/head. She gets up and I think they fight a bit more and she pushes him. He falls on top of the spiked helmet from earlier and crawls away.
The parents come home and she doesn’t respond to them and gets her bike to leave, all the while they’re yelling that she drank all the alcohol.
A closeup of the boy’s face is seen staring off into space and we realize he is dead. A hand reaches for his glasses and we see the little sister putting them on. She sits herself down in front of the computer/radio and puts on headphones as the scene freezes and fades out.