I was your son, slightly older at 11 and the first time I watched a film that wasnt live on telly was "Never Ending Story" a PG film
We borrowed it on video and all the neighbours piled in to watch it (we hired a VHS recorder) and charged neighbours and friends for "cinema" space - 10p a child, 20p adult per film, drinks provided (fizzy drinks), - bought in quantity from cash and carry and stored in shed, bring a mug with you would cost 5p per mug so the living room was always packed, people on the floor bring your own cushion/deckchair,
Before anyone berates my family for charging, it was way cheaper for all than one cinema ticket and it covered the costs incurred (rentals, tape rentals,
Anyhow the afternoon show was the very first one aimed for the younger ones, I didn't sleep well for over a week, due to fears about the dragon. I haven't dared to watch it since.
Another night my mum woke to a lot of shoving and tussling from my room - we had watched The Golden Child - that night, my friend was staying over and we were both terrified that the devil was coming to get us so moved the bed up against the door. Sealed over the keyhole and had moved wardrobe in front of the window.
Keep reassuring him no matter how long it may take.
Also v briefly, I recall the time that my mum picked up the tape in the rental shop, sadly the cassette inside didn't match the cover and no-one noticed until it was starting.
It was very quickly grabbed and removed from the player when we as kids were sitting waiting to see Who Framed Roger Rabbit - lets just say the cassette contained a lot of rodgering and definitely not suitable for kids.