A funny thing happened at the Edinburgh Fringe Festival the other day. Well, I should hope so, given the prices comedians are charging. Boom, boom. Thank you, I'm available for bookings. No really, this was funny in the funny-unusual sense.

Justin Moorhouse, who played Kenny from Phoenix Nights, the character who spent most of the time sporting unwashable tiger face-paint, saw a 10--year-old girl in his audience and suggested that she and her parents leave. Now you'd think comedians would be grateful for any fans, but Moorhouse knew his show better than them and clearly felt that it wasn't suitable. And he was right. Very funny, but also very rude. And no tiger face-painting at all.

This issue of suitability of shows has vexed me for a while. At the Latitude Festival recently the programme took the innovative step of giving film-style certificates to acts. Scott Capurro and Frankie Boyle were 15s (personally I'd make Boyle a 21 certificate) while others were clearly marked as family-friendly. Quite how this was enforced, when middle class feral children were left to wander freely around the site, I don't know, but at least it was a step in the right direction.

The only time I've ever seen this done in Edinburgh was with spoof children's entertainer Jeremy Lion. Because his poster featured party balloons and funny hats it also clearly stated that the show was for 16-year-olds and up, so that no misguided mums took their toddlers along to see a depressed alcoholic drink a dozen glasses of red wine and a suitcase full of miniature spirits and go through an existential crisis onstage. In London I've been to Russell Brand gigs where the ticket stubs say that the shows are for over-18s only, but I'm sure I've seen people there who have to be up early for school the next day and I don't mean teachers.

It is a complex issue. As someone said to me regarding unsuitable material "if they get it it doesn't matter and if they don't get it it doesn't matter either". Which is both profound and wrong. I wouldn't like to be the parent who had to explain some of Andrew Lawrence's humanity-hating rants to an inquisitive 11-year-old.

Maybe comedy should introduce a strict and proper ratings policy. I'd happily head the BBFC – the British Board of Funny Censors. Sometimes comedians love it when kids are sitting in the front row. but it can also have mixed results. Richard Herring regularly used to accuse someone in his audience of resembling a paedophile and I'm not sure how that would have gone down if he had chanced upon a father taking his children for a night out.

There might be a downside to a ratings policy if it goes too far though. I remember Johnny Vegas having great fun with a mum who had brought her kids along, suggesting that she had calculated that buying them tickets was cheaper than paying a babysitter. Jason Byrne, whose act also largely involves interacting with the crowd, often has a fine old time picking on parents. I'm not sure how much the mums and dads appreciate being the butt of jokes, but I bet the kids – at least the ones who haven't hit the embarrassed-by-everything adolescent stage – love it. Byrne might be an adult act, but if they banned children from his gigs they wouldn't be anywhere near as funny.