The cruise ship is plying a new route to Okinawa from Hong Kong via Nansha, Guangdong, until November, when it will relocate to Shenzhen to make way for the first of the megaships three times its size that owner Genting hopes will capture the expanding Asian market.

Japan’s finest beaches and crystal-clear waters are a siren call to a tired parent who loves his little urchins but harbours a primal fear about being confined with them for seven days in a cabin smaller than a Hong Kong flat.

Hair pulling, face scratching, and high-pitched wailing are all things I like to give a little space.

The optimist in me hopes that, perhaps, at sea no one can hear them scream.

As we arrive at Harbour City, drenched by an untimely downpour, the advantages to the life aquatic emerge. With no weight limit, we have packed bags so large and heavy they might challenge Trident himself. We dump them at a counter and forget them until we reach our cabin, where Alice deduces triumphantly, “The SHIP is the hotel!”.

Not for us such dilemmas as whether to pack an essential like Girl Ted over frivolous items like clothes for Daddy. And no cramped, embarrassing flight in which two dwarves with air rage trample over our laps.

Instead, we marvel at a vessel that, at 269 metres long, is to a toddler so incomprehensibly huge it is hard to accept it does not qualify as its own land mass, a floating continent for its 4,000 passengers and crew.

It becomes our mother ship, fattening us up with nutrient-rich all-you-can-eat buffets and nurturing us as we swim in its amniotic swimming pools (there are three, one with jacuzzis and classical statues).

Being a young family – a minority aboard – is an advantage. While others gamble, or watch shows such as ‘Blonde Bombshells’, we often have the pools to ourselves.

Meal times – once daunting – are a breeze. Thirteen restaurants and bars, some with free buffets, dispel fears about wasting food or cash on unpredictable palates.

There are magical things like ice cream parties and balloon sculpting and cookie decorating and a mariachi band that serenades Clara with Twinkle, Twinkle, Little Star.

Staff smile even in the face of parenting atrocities.

And in the warm belly of the Virgo, the girls begin to grow. Previously shy Alice attends a big girl’s party, swims unaccompanied and graduates to high-fiving the line-dancing Chinese ladies in the lobby.

Our balcony offers a front row seat to a never-ending show. Flying fish skip through the water, birds dive and waves wash away the years of ancient parents as the green waters of the East China Sea turn an aquamarine blue.

The mother ship docks, loosening its umbilical cord to allow us ashore, and we step into brave new worlds of sparkling seas and ancient temples.

In Naha, the Okinawan capital, young feet wander along 15th century paths at Shurijo Castle Park, a World Heritage Site that transports us through ancient gates and stonework to the splendours of the Ryukyu kingdom.

They speed up as we dive into a temple of modernity, a dollar-store mall full of Hello Kitty, blinking lights and frenzied shoppers seeking tax-free bargains – the kind of chaos Japan does so well.

We head for dinner along Kokusai Dori (International Avenue), a 2km stretch of restaurants and shops, and disappear past a man selling plastic chickens into a ramen joint where a two-man band belt out Okinawan classics with a drum and a sanshin (a three-string guitar with a snakeskin soundbox).

We watch in horror as Clara rips off her shirt and streaks onto the stage, demanding her turn on the drum. But it is okay. We are in Okinawa and stage invasions by topless toddlers are not only tolerated but celebrated. As the band becomes a trio we savour the free baby-sitting, nibble on spring onions fried in batter and wonder whether it is Okinawans’ diet or relaxed attitude that is the secret to their famed longevity.

Our guide on Miyako island says it is the diet, with ingredients like shekwasha (flat lemon), threaded seaweed, and bean curd warding off complaints from high blood pressure to thrombosis. Hedging his bets, he advises mixing shekwasha with alcohol, then produces a sanshin and serenades us as we trundle from beach to beach.

We bypass Maihama, where most tours stop, to search for a more private paradise, finding it at Aragusuku (New Castle) beach, where lump coral grows in shallow waters near the shore, perfect for a toddler’s first foray into the underwater world.

There is a laidback vibe here, with one shack selling noodles, another renting snorkels and floats. Crucially, there are tables with sunshades for rent (1,000 yen).

It is Alice’s first go at snorkelling, and while her head is too small for her mask, the water is clear enough to see the clownfish and wrasse from her perch on Daddy’s head. She sees them more clearly than her steer, who is struggling a little with her ‘water down the snorkel’ game.

When the sun proves too much (“Why Daddy back purple?”) we drive to the Shimoji Ponds – two sinkholes connected to the sea by a 10-metre-wide tunnel that have given birth to various legends and are used to train cave divers. We gaze across Cape Higashi where Maiwa – a 9-metre tsunami that hit in 1771 – scattered rocks far from the shore where they once sat.

We come to rest on Painagama (South Beach), a short walk from the dock. We have it to ourselves and the girls delight in shallow water so clear it could not be seen if not for their splashing.

In Nansha, we visit Dajiao Mountain and shelter from the intense heat at Tianhou Temple, which resembles the Forbidden City and honours Mazu, goddess of the sea.

There are many steps for the girls to be carried up and it is not long before those carrying them dissolve into a pool of sweat. “Why Daddy wet?” asks Alice. “Daddy gross,” says Mommy.

As the children play in the shadows of the magnificent halls, Mommy donates 10 yuan for a fortune stick, perhaps hoping it foretells a future involving a less sweaty husband.

A turtle pond catches Clara’s eye and we linger to take the animals’ pictures and coo at their cuteness. Other tourists photograph the girls, clucking that they resemble a popular doll.

We head to Panyu’s Lotus Hill, home to a Buddhist temple with a 40-metre golden statue of the Goddess of Mercy. It is an hour’s drive and the wet patches on Daddy’s shorts – “Daddy wee himself?” – are dry by the time we arrive and order steamed milk, a Cantonese dessert, at the café. The dessert spills on the shorts.

Oscar, our guide, is a revelation with the girls, gamely holding hands and dangling them over the temple’s vertigo-inducing walls as their parents concentrate on sneaking selfies with unsuspecting monks.

Exhausted, we collapse into the mother ship’s loving bosom, suckling on its mojitos one last night.

It is raining as hard as our day of departure when the Virgo’s umbilical cord finally detaches, delivering us to Tsim Sha Tsui.

Yet as we collect the giant afterbirth that is our luggage and head for home, we look at our city as if for the first time, through the excited eyes of a child.

We make our way through its crowds and buzz and technicolour madness, and it is not hard to imagine this is just the latest stop on our adventure.

Andrew Raine