Take Aliens. An 18-certificate film, children are lawfully not allowed to see it. Fine. So why do we let children as young as eight into the Trocadero's 'Alien War', based on the film?
'Alien War' is an action event not for the faint-hearted, warns the management. This is the stuff that turns grown men into quivering wrecks.
You are on a guided tour of the Weyland Utani station, a tour that goes horribly wrong.
An alien has escaped and the area must be evacuated. It is almost pitch-dark. Ten of you huddle in the corner of a room not much bigger than the average bathroom.
The room fills with smoke and the guide fires shots into the darkness. You don't know where the alien will come from, but you know it will come. There's no way out and, certainly, no cushion to hide behind.
Attracted by the generous pounds 4 saving on a family ticket, Aliens-buff Sally Howard, 40, from Wallington in Surrey, visited the attraction with her two eight-year-old girls.
Even she was petrified. Although the girls had seen the films, they were terrified when they 'relived the nightmare', as the publicity invited.
Mum spent most of the 20 minutes reassuring them that they would survive the experience. Reassurances in vain, both wet themselves.
To their credit, the staff are careful to remove anyone who looks as though they are having a bad time of it. And many are pulled out after the briefing, according to 'Alien War' assistant manageress Caroline Kennedy. She tells of someone found in the foetal position, rocking. On another occasion, an ambulance had to be called for a woman who 'lost it'.
Even officers from the Met who visited 'Alien War' came out feeling very sorry for themselves indeed. Psychologists agree that children can be traumatised by films - not just by the images they see, but by those their imagination creates afterwards.
It follows, then, that the same should apply to 'Alien War'. If seeing the film can be traumatic, is not participating more so?
While adults who come out terrified can have a stiff drink and rationalise that it was 'all in good fun', children receive a distorted image of emotions they have not yet experienced. And we can all remember a film that gave us nightmares as a child.
So if legislation exists to protect children from potentially disturbing films, why not also for other forms of visual entertainment?