The second time this happens you produce a tube of Factor 100 and mime rubbing motions over the children's shoulders. But it doesn't impress the old know-alls: they go away making it clear that their opinion of British parents remains about as high as their opinion of British football fans.
Somehow, in Britain, you don't think it's so important. Last year the financial implications of taking two children and a new baby anywhere near foreign sand persuaded us instead to spend a fortnight at St David's in Dyfed. Since the chances of encountering much ultra-violet in the land the sun forgot are slim, one pleasure of holidaying there is that you need to pack fewer cosmetics.
The evening that we drove down the M4, however, stopping at most of the services on the way to attend to bladders or dab vomit off the car seats, the sky was glowing redder than the set of Reservoir Dogs. To compensate for the nightmare five-hour journey, we promised the children that the next day would be spent on the beach.
The following morning wasn't as glorious as the sky had advertised. A haze reduced the sun to a blur, and a crisp wind whipped off the sea; it was typical Wales in July. Whatever the weather, though, a day on the sand is no hardship in St David's. The city is surrounded by better beaches than any the Mediterranean can offer: great, white expanses, which, if you are prepared to haul push- chairs and deck chairs over fields and stiles, you can have almost to yourself.
We had packed windbreaks, wind-cheaters, wind-shields - no need for sun-block, we thought - and drove to Nolton Haven, about eight miles from St David's cathedral. There, we spent the day building castles, playing beach Olympics (putt the pebble, seaweed javelin) and picking the sand out of sandwiches. We hardly noticed that our elder son had been without his shirt most of the time.
That night, in the bath, it became clear that, though the sun had hardly peeped from behind the haze, he had been burnt to a crisp. In bed he could hardly move. Next morning he looked like a victim of the bubonic plague, skin bubbling, sores oozing a liquid the colour and consistency of honey.
On our second day, his shoulders were not the only thing blistering. The weather had turned glorious, no wind, the view across St Brides Bay so clear that you could see every detail of the oil installations outside Milton Haven. My wife suggested I take the boy to the doctor's, while she took the other children first to the chemist to stock up on sun- block, then to the beach. I thought she was just being organised. In fact, she could foresee the humiliation.
At the local surgery, I asked if the GP saw holidaymakers without an appointment. The receptionist smirked. 'Sunburn is it?' 'Er, well, er, you know.' 'Join the queue then, love,' she said with a knowing chuckle.
On a day when west Wales was enjoying the kind of weather normally associated with the south of France, the waiting room was packed with people who longed to be elsewhere. A complex system of buzzers and numbers alerted you to your turn, which a cunning old local used to his advantage, jumping the queue ahead of a Boy Scout with an injured ankle.
The Scout's Akela sighed ostentatiously, but felt it wise not to argue with a local. 'Bloody tripped getting out of the minibus the moment we arrived at the camp site,' he told the waiting room. 'Bloody idiot. I've got better things to do than sit around here.'
The boy pinked as his leader spoke, and buried his head deep in an ancient edition of Beano. He need not have worried. Seconds later, the door opened and another Scout from the same pack appeared, clutching a fistful of reddening lavatory paper to his head. He was accompanied by another leader. The Scout with the twisted ankle smiled in solidarity.
'Bloody hell, Watson, what happened?' said the Akela, his blood pressure rising to combustible levels.
'Sorry, Akela,' said the new arrival. 'Davies was bashing in a tent peg and the end came off his mallet. Hit me on the head.'
'Bloody, bloody Davies,' said Akela to the very bloody Watson.
He had barely suppressed his rage when a third Scout came into the surgery, supported by yet another leader. He explained to an apoplectic Akela that the boy had burnt his hands on a rope while erecting the marquee.
'What a bloody start to bloody camp]' Akela roared. 'God knows what's going to happen when we go canoeing tomorrow.'
Given our fellow sufferers' ailments, I felt less ashamed about wasting NHS resources. Indeed the doctor, when he finally examined our boy's angry shoulders, kept the lecture to a minimum. Very pale skin, he pointed out, shouldn't be anywhere near the sun. Shouldn't be anywhere near the cloud, come to that. I nodded knowingly, then shamelessly blamed my wife.
There wasn't any need to follow the doctor's advice and keep the boy away from the sun for the rest of our holiday. The sun kept away from us, disappearing behind a thick wad of mist that swept and swirled in from the sea.
This enabled us to indulge in the activity for which Wales provides unsurpassed opportunity: sitting in the car in a castle car park, eating a picnic with the windows steamed up, children in the back asking when they'll be having fun and parents in the front telling them to stop being so sour, this is a holiday after all.
After a couple of days, even the pleasures of castle car parks began to pall. Fortunately St David's is designed for rotten weather. Places abound which, for a couple of quid, will relieve you of wet-weather boredom for at least 20 minutes. For instance, at several marine life centres crabs can be picked up and surly looking lobsters, with their claws rubber-banded, can be prodded and pawed. And about 15 miles away, just outside Haverfordwest, we discovered Oakwood.
This is a theme park, the kind of place that, before you had children, you would rant about: burying prime farmland under mechanical rides, turning proud agricultural workers into Burger Chefs, transforming 80 acres of beautiful Wales into ersatz Florida. Oddly, the moment your children reach four and the weather's not so fab, you find yourself at the turnstile handing over the pounds 18 family entrance fee, hoping you don't meet anyone you know.
After a day riding the swinging pirate galleon, whooping down the toboggan run, dragging tired and reluctant offspring on their seventh ride on the roller coaster, I was evangelical. What a place, I told everyone I met. Haven't had so much fun for decades. And, best of all, no need for sun-block.
Oakwood Adventure and Leisure Park, Canaston Bridge, near Narberth, Pembrokeshire SA67 8DE (0834 891376).
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