If a mother's place is in the wrong, I was there once again. The surf was up, the waves were empty - and I'd forgotten not only the swimming trunks, but the wetsuits too. "Oh mum. I want to go in." Jack couldn't decide where to look. Should he gaze reproachfully inland, at useless forgetful me, or enviously seaward, where his hardy 12-year-old friend, Tyber, glided wetsuit-less down the icy Atlantic rollers? I prepared for a good half an hour of demands that I somehow magically alter the sea temperature upwards and/or knit a wetsuit out of some pebbles and a bit of bladderwrack. But then, quite suddenly, Jack grew up.
"What the heck," he said, with a nonchalant shrug. "I can cope with a bit of cold." And with that, he pulled off his T-shirt, jeans and socks, picked up his board, and ran into the freezing waves. In his pants. You won't see that in Riding Giants.
A couple of years earlier, Jack had been the sort of child who saw getting a bit of wet sand in his shoe as a potentially soul-scarring incident. But holidaying in west Wales makes a man of you. In western Cornwall - to which Pembrokeshire's rugged limestone coastline is close topographical cousin - you'll eat at Rick Stein's, ride a custom surfboard, and party on the beach with your friends from Chelsea. In Pembrokeshire, you drink tea from a thermos, hire a dinged foamie from the man by the lifeboat ramp, and go in the sea in your pants. Who needs Rock, when you've got rocks?
We first went to St David's, at the top end of St Bride's Bay in Pembrokeshire Coast National Park, three years ago, at the invitation of a close friend who has holidayed there since her childhood. I was uncertain - Wales for the summer? Wouldn't that mean rain, bad food, worse accommodation? Wouldn't Cornwall be a better place to dip our toes in surfing's waters?
At first, it seemed I was right. The journey from London - M4 entirely shut after Bristol, achingly slow crawl through the Forest of Dean - took nine hours. (I've got to Dubai quicker.) St David's was pretty enough, our cottage sweetly whitewashed and slate-roofed, but all Jack and his younger brother Tom were interested in was going to Whitesands beach, five minutes' drive away. It was empty, grey, the sea at low evening tide a gunmetal strip on the horizon. I sat shivering on a blanket, under an umbrella and a haze of rain, yelling at them not to get their trousers wet. They did get wet. So did my bum. I wanted to go home.
But the next day, we woke to find that the peninsula's microclimate had done its stuff, and the sun was sprinkling benignly upon a dreamlike landscape of turf-topped cliffs, mossy coves and glittering silver seas. We squeezed ourselves for the first time into wetsuits - much softer than the smelly, rigid straitjackets I remembered from my teenage windsurfing attempts - and went back to the beach, now a heart-stopping arc of bright, ermine-soft sand smacked by effervescent green waves. The boys headed off for a surf lesson; I waded out with a £20 bodyboard under my arm, turned and waited. By the time the first wave had picked me up and cast me, squealing, back on the beach, I was in love.
It was a coup de foudre, and we've kept going back for more. Our holidays in Pembrokeshire have changed my sons from children who regarded seas anything other than Mediterranean-balmy with deep suspicion, to salty-haired tough nuts who have to be lassoed out of the foamy brine. Here they've climbed granite rock faces 25 times their own height, had wild ponies nick peanut butter sandwiches from their backpacks, and, in the name of a sport called coasteering, jumped gleefully into the sea from ledges teetering 30ft up a cliff.
It's not all muscle-building, though. The land here is also inescapably spiritual. The brackeny, nibbled heaths that edge the coast and the gorse-sweetened volcanic cairns inland are chequered with Neolithic burial chambers, Bronze Age stone circles, Celtic wells and ruined medieval chapels. And the heart of the park, geographically and morally, is sanctified ground - St David's was the home of Wales's ascetic 6th-century patron saint.
Known as "the water-drinker", partly because he wouldn't touch beer, and partly because springs tended to appear in his wake, David founded a monastery in what was then an unloved, marshy river valley. Barring the odd missionary trip to Ireland, he lived there for 100 years (all that water must have been good for him).
Well over a millennium later, the monastery is long gone, but the community that grew up around it survives. "Britain's smallest city" - it gained its grandiose title in 1995 - is actually no more than a close-set village of 2,000 souls, two pubs, and one curving street, which cups the surprising secret of its city status: a glorious, honey-coloured cathedral that sits in a hollow at its centre like a drop of architectural nectar.
While Tenby to the south is all kiss-me-quick and candyfloss, St David's is a gentle hug and a warm Welshcake. Apart from August, when rhinoceros-herds of 4x4s shoulder through on the way to the beach, it is a misty, contemplative place, one that has survived on a piecemeal diet of God and the sea for centuries. Where pilgrims once knelt at Dewi Sant's resting place, now tourists take pictures of the churchyard and buy local pottery. Where once the lifeboat station looked out for trawlers and wherries sailing lime and lead up the coast, now it keeps an eye on pleasure boats chugging birdwatchers out to the puffin colonies on Skomer Island.
Its joys are many. Go out of season and you'll have Whitesands to yourself; we've surfed alone there in October while rain swept over a few thoughtful dogs, who watched us from the safety of the cliff-backed shore. During school holidays, the beach's Blue Flag cleanliness, café and lifeguards attract an ever-increasing throng, and every wavelet is lined with serried ranks of excitable bodyboarders. But even in high summer, it's easy enough to escape. Walk a few hundred yards up the narrow, heather-lined coastal path - an attraction in its own right for ramblers and naturalists - and you'll find quiet, sandy coves gnawed out of the purple cliffs by a sea that's rolled all the way in from America. Drive up the coast a little way, towards the direction of Fishguard and the ferry to Ireland, and there are still quieter spots, pebbled strands we've had entirely to ourselves in the middle of August.
Wherever you go, though, the wild, adventure-playground quality of the place is ever-present. At the southern end of St Bride's Bay is Druidston beach, accessible only down narrow bridle-paths from the coastal road. At low tide, its mile-long, foam-flecked sands resemble something out of Ryan's Daughter, and regularly play host to galloping horses fresh from the local stables. It was here I got back on a horse for the first time since smashing my shoulder in a riding accident five years earlier. "Is he good?" I asked. "Because I have a tendency to fall off..." "Oh yes," called the ride leader, as myself and horse bounded off towards infinity. He was good, though: we tore at something approaching light speed towards the cliffs at the far end, but as I closed my eyes and prayed to the equine deities, he wheeled gently and cantered his exhilarated, panting burden back to the rest of the ride. Then we swayed sleepily home in a line, climbing up the bridle-path between hedgerows thick with flowers and the huge, hairy leaves of wild gunnera.
On the drive back we stopped at the harbour beach of Nolton Haven, where Tom found a seal skull with fish-spearing teeth and blanched clean by the ocean. In livelier days, its owner probably lolled with several hundred mates on the shores of Ramsey Island, a grassy nature reserve about a mile offshore from St David's, and a popular boat-trip destination.
Not that you have to be seaborne to see seals. We went climbing one windy, sun-sprinkled afternoon, out where the granite fist of St David's Head thrusts into the sea. Our guide was a gentle, long-haired twentysomething called Sam, a young man who loved the area with an extraordinary intimacy - he had, in his time, paddled his surfboard all the way to Ramsey to spend the night there with just gannets and moonlight for company. After clambering down a series of boulders like a giant stepladder, we were helping set up the ropes for the first climb. Sam tore off a fleshy clump of samphire growing from a crack in the rock and gave it to Jack to chew on, then pointed 100ft down to the suck and swell of the water below. "There's a seal, look," he said, "giving us the eye."
Indeed it was, its wet-labrador head tilted quizzically as it considered these strange ape-like creatures clambering about on the rocks: little monkeys turning, slowly but surely, into men.
The nearest railway station to St David's and Whitesand Bay is at Haverfordwest. Contact National Rail Enquiries (08457 484950; www.nationalrail.co.uk) to find out timetables and fares.
Ty Gwilym Holiday Cottages, St David's ( www.tygwilymholidaycottages.co.uk). Cottages start at £220 per week.
Surfboards can be hired from Ma Simes Surf Hut, 28 High Street, St David's (01437 720433; www.masimes.co.uk) for £10 per day. Wetsuit hire from £6 per day.
Tyr y Felin Adventure, St David's (01437 721611; www.tyf.com) offers climbing, surfing, kayaking and coasteering instruction.
East Nolton Stables, Nolton (01437 710 360; www.nolton stables.com) offers horse riding at Druidston. Rides start at £22.50 per hour. Pembrokeshire Coast National Park Visitor Centre (01437 720392; www.stdavids. pembrokeshirecoast. org.uk).
Pembrokeshire Tourism: 01348 873484; www.visitpembrokeshire.com
Wales Tourist Board: 08708 300 306; www.visitwales.co.uk