These aren't topics I'd willingly ' />

Thanks to Speights and Toyota I've had to explain venereal disease and bestiality to my 8 and 10-year-old sons.

These aren't topics I'd willingly have raised at such a tender age, but some clever clogs advertising types didn't give me much choice.

We were stopped at the traffic lights opposite a Speights billboard showing a young dude in an oilskin asking an old dude in an oilskin how many DVDs he had.

The mate replies "That's a bit personal, boy."

My 10-year-old piped up from the back seat: "I don't get that."

My own education on sexually transmitted diseases occurred when a visiting VD specialist showed his collection of clinical colourslides to my seventh-form class of awestruck schoolgirls. I hadn't anticipated passing on any of this knowledge to my sons before their teens. The husband and I exchanged one of those do-we-really-want-to-go-there glances.

Believing that honesty is the best policy I launched into a very brief explanation. The advertisement was a pun on the word VD, which stands for venereal disease, an infection you get by having sex with someone. I emphasised that it was not polite to ask someone if they had VD (and hoped like hell the boys didn't repeat this to any of their less-informed school friends). There was silence from the back seat.

A couple of weeks later the two boys were playing a noisy game of Lego wars when my maternal radar registered that they were chanting "sheep shagger" at each other. I was gobsmacked. Where had this come from?

The 10-year-old was surprised that I had to ask. "The Toyota ad."

Of course. Two randy bulls raging around in a ute apply this delightful epithet to a passing ram. Having taught a whole generation of Kiwi kids to swear by way of the "bugger dog," Toyota has introduced them to yet another inappropriate expression. Fabulous. Good one Toyota. (Although I thought the bugger ad was very funny, I was less enthused about its impact on my sons' vocabulary).

This time I tried the easy way out, saying it was very rude to call anyone a sheep shagger. A friend got away with this explanation, but my two sons appear to have inherited the gene for journalistic nosiness and weren't so easily fobbed off.

"But why is it rude?" they demanded.

So I tried the brutally frank approach instead. "Because it means someone who has sex with a sheep."

They looked suitably appalled and we haven't heard the expression since.

I don't feel strongly enough about the Toyota ad to complain to the Advertising Standards Authority but at least 20 other viewers have. By a majority verdict the complaints failed but even if the complaint had been upheld it would have been too late for the legions of parents who have to cope with the fallout.

Possibly the ad was penned by some young hotshot copywriter who thought he or she was being terrifically funny. Or maybe it was the work of an older (t)wit whose kids are too young to pick up the sheep shagger reference.

Perhaps advertising types would be less risque if they were forced to front up to a bunch of inquisitive kids and explain why the term sheep shagger isn't in polite use.

Realistically, I know it won't be long before some other ad introduces my kids to yet another X-rated topic.

I'm not too concerned about the "No rubba no hubba hubba" campaign because it usually airs after youngsters are in bed. Besides, they already know what condoms are. Been there, explained that, after a young friend found one in a park.

However, I do confess to crossing my fingers every time those Viagra adverts appear on early evening television. Impotence is not a subject I wish to explore with children if I can avoid it.

As it is, plenty of other intimate bodily functions get an airing. After I returned from a public toilet grumbling about the long queues my child informed me this was because 30 per cent of New Zealand women were incontinent. He'd picked up this little gem off an advert for incontinence aids.

I suppose I should be grateful he's learning something useful.

My childhood memories of TV adverts are of cute little characters like Ches and Dale the singing cheese men and that irritating woman who demonstrated how Sunlight Liquid left plates squeaky clean.

I suppose I should be grateful the Viagra ad doesn't have a catchy tune, or they'd be singing that in public the same way they belt out, "The Warehouse, The Warehouse, where everyone gets a bargain" or "Pizza Hut, 83 83 83" - although the youngest occasionally sings "Alleluia 83, 83, 83", which is rather puzzling in a decidedly secular household.

We've tried to raise media-savvy kids by constantly telling them advertising is a con designed to make them want things they don't need or can't afford.

But I'm not at all sure the message has been received, especially when I hear them singing along to the adverts on TV. Then I console myself with the thought that maybe they'll grow up to be hugely talented and vastly overpaid ad-men who will keep me in the style I'd like to become accustomed to. Yeah, right.

* Amanda Cropp is a journalist and a mother of two.