So, I'm wandering around my nearest out-of-town supermarket - absolute barn of a place, and never anybody to hand when you can't find the tinned coconut milk - and for once I have my nine-year-old son in tow.

Knowing he loves Batman and The Simpsons I whisk him up to what they probably don't call the "mezzanine level" to look at some clothes I spotted on an earlier sortie. These are: a six-pack of Simpsons socks and a baseball cap with the famous bat logo on it.

"They're horrible," he says when we arrive in hosiery. "Ugh! No, dad." At the hats, the same: "No chance" followed by "Yuk!". (At least I think it's "Yuk!". We're at that stage, he and I, where I still wish to remain ignorant about the swear words he knows. Sure the view's not great when you have your head stuck in the sand, but at least it stops you hearing things you might have to talk to a teacher about.)

What is odd is that back in the grown-up world, companies are trying to do for adults what the supermarket signally fails to do for my son: namely, persuade them it is a good idea to wear clothes emblazoned with images of cartoon heroes. And it is working.

Step into a high-street fashion chain selling shoes, for instance, and you will find a line of baseball boots and sneakers being sold under the label DC Comics X Converse. They are mostly Converse All-Stars printed with various images of Batman or his nemesis The Joker, or covered with that same bat logo. They have been out for a while now and potential customers can even customise their own pair using images from the Arkham City series of Batman computer games.

Topman, meanwhile, is selling a range of T-shirts, bags and hoodies under the label Hype X The Simpsons. Hype, by the way, is a fashion brand and for those Herald readers who do not own a telly, The Simpsons are a yellow cartoon family whose patriarch, Homer, lives on beer and doughnuts. As you would expect, the T-shirts are pleasingly garish as they do not really do neutral tones in The Simpsons. But, again, they are being purchased by adults who can think for themselves and dress accordingly.

It is that "X" that's all-important here, of course. In mathematics it is a multiplier, but in fashion terms it also signifies collaboration, crossover and all-round coolness, as well as exclusivity and rarity. Those last three explain its increasingly common use by labels and retailers. They have cottoned on to the fact that the 24th letter of the alphabet morphs neatly into the symbol that sits three rows above it on a typewriter keyboard - the pound sign. Clever, eh?

Back in the supermarket, The Simpsons and Batman offerings are resolutely X-less. Perhaps, even aged nine, my son can sense the lack and makes his fashion choice accordingly. As a result, he goes home hatless and sockless. I, on the other hand, do eventually find the tinned coconut milk.