"Don't be afraid" said his nine-year-old sister, Anna. "They are more afraid of you than you of them."

There was excitement in the air. It was time for their debut on a coral reef.Until now, they had always stayed at the surface when I disappeared under the sea, looking like a Christmas tree with all my photographic gear. But they had practised with snorkel and mask in the pool, and now they were ready for their first visit.

The Red Sea was dead calm. It was December, and the water was quite cool. "Watch out for the yellow corals that look like tree branches," I told the children. "They are fire coral and burn like jellyfish. Don't touch any fish lying still on the bottom. Don't swim too close to the corals or you'll get cuts." My instructions were not exactly reassuring for two nervous beginners. It was difficult to say who was most excited by the occasion. For a while it looked as if we wouldn't even get out to the reef. The water was too cold, their masks were leaking, and the salt water was hurting their eyes. But I was determined to get some nice shots of the kids swimming among the corals.

After some persuasion from me, Johan and Anna went out from the beach towards the reef, with me ahead, loaded with camera equipment, pulling my sceptical offspring on a rubber inner-tube.

Out at the reef edge I paused to put my flippers on. Johan couldn't wait, and jumped in the water to get his first view of the corals. He came up, pulled the snorkel out of his mouth and yelled: "Dad I saw a big fish".

Then he started spitting and spluttering when a mouthful of salt water found its way into his mouth. Crying, he climbed back on the tube. "Dad, I want to go home." Anna looked on with contempt.

Finally I was ready. Curiosity overcame Johan's temporary setback, and he threw himself in the water and dived like a stone to the sea bed. Anna, who always calmly contemplated any risks before she did anything, looked down carefully into the water before she slowly glided down.

Soon the screams of two thrilled children were heard through the water. "Dad, dad, you must come over here. I saw a fish full of spines with big, kind eyes."

"No, come over here, I saw a shark."

Next, I held their hands and swam out with them into deeper water. A school of barracuda shot away in front of us. A group of big capricorn fish slowly glided past while the children pointed and shouted. The sergeant majors, used to divers, came close to see if any titbits were to be offered.

I had dreamed about getting photographs of the children swimming in a beautiful coral landscape, and now I decided it was time to organise some pictures. But it was not easy to direct two excited kids.

"Don't dive until I am in position and give you the sign. Don't look into the camera. Keep your arms still," I instructed. I dived, composed the corals nicely in the viewfinder, and waited for the models. Nothing happened.

When I had turned blue in the face (I did not have scuba equipment), I went back up. There I found the kids sitting on the tube with gloomy faces. They were feeling cold and wanted to go home.

"Please, just a few shots," I pleaded.

"Okay, but just a few." The children did not want to disappoint me.

A beautiful sea anemone with its clownfish, just below the reef edge, was the perfect lure to make the children dive. Excited, they went down to study the clownfish more closely. Suddenly, Johan pulled his hand from the anemone with a scream, and went up to the surface like a rocket.

"Dad, the fish bit my finger," he complained.

Patiently, I explained that the clownfish was only protecting his territory against an intruder.

"This is what happens when you get too close."

When finally I thought I might have got some nice pictures, and the children had grown tired and cold, we returned to the shore.

"The clownfish were so nice, dad," Anna said, trying to encourage me.

"I saw a shark, dad," said Johan.

It happens infrequently, but once in a while you come across a site, tucked away on the far side of a point perhaps, or in a secluded cove, which makes you thankful that you're a diver.