The lagoon is, by turns, turquoise, cyan and cerulean. It is a scene of other-worldly beauty. And Grace is screaming her head off.

"I'm not going swimming. I'm scared!!!" she wails.

"But, honey, there's why we're here, to swim and snorkel and dive bomb off the boat," I say, calmly.

"There might be SHARKS," she hollers, eyes wide with horror.

We live in one of the most shark-infested countries in the world; she's frightened of swimming in one of the least.

"Of course there are sharks in Tahiti," our captain, Laurent, says. "But here, they are reef sharks. They won't hurt you."

Unassuaged, Grace sulks for the first four days of our week-long break.

Meanwhile, Jason, Taj and I explore an underwater wonderland, with a dazzling array of tropical fish.

Laurent takes us to a stingray colony, where he jumps into the water calling, "Come on Taj!" Our son clings to the captain, as they feed the stingers: "Hello ladies," Laurent says, their undulating bodies snuggling into him. "Mum, Dad! Can you take a photo?" Taj asks. "Can't wait to show the boys at school."

Grace is nonplussed by the tale. "Hmf," she says. "I don't like stingrays. Taj, you're an idiot."

We try to take her fishing. But all we catch are parasitic fish, which feed off the sharks. Once on deck, they explode into pools of blood.

It appears as if there's been a murder; we throw the corpses overboard. Minutes later, one shark laps the boat. Then another. And another. Soon, eight black-tipped reef sharks are circling our vessel.

Grace sits on the edge: "Wow. They're kind of beautiful," she says, mesmerised. Elegant and athletic, they slice the water. We watch them for hours before drifting into a deep sleep.

The following morning, Grace has an epiphany: "I'm ready to go into the water."

"After seeing what's in there? Are you kidding?" I ask, incredulous.

"Laurent says they won't hurt me, and they seem quite nice," she says. "I guess I'm used to the idea now."

In her nine-year-old way, what she's describing is exposure therapy. This is used by psychologists to treat anxiety disorders – the patient is gradually exposed to something they fear, in a safe environment.

It works a treat with children. That afternoon, I hold Grace's hand as we snorkel through the Coral Garden. Barely a metre deep, this is a channel full of tropical fish: a current propels you along its length.

"Mum, that was the best," Grace beams, fears forgotten. "Can we go and swim with the sharkies, next?" "Let's take it one step at a time, darling," I say.

Kids' irrational fears can ruin a family holiday. Why not try a spot of exposure therapy? It's infinitely better than feeding them to the sharks.

Tracey Spicer and family sailed in Tahiti courtesy of moorings.com.au.