He hasn't been seen since.

For his parents, Alice and Philip senior, and his siblings Mary, Sandra, Helen, Suzanne and Eoin, the last two decades have been extremely difficult.

"Every single day the thought of him is there, " said Alice Cairns, in an interview with the Sunday Tribune. "In many ways, every bit of that day is as fresh in my memory as if it was only yesterday.

But then when I think of when I last saw him, it seems a terribly long time ago. If I had known then that in 20 years' time Philip would not have come back and that nothing would have been found, I couldn't have lived. I simply couldn't have got through it. But you get up every day because you have to, and you just get on. You've no other choice."

Thursday 23 October 1986 was a day like any other in the Cairns household. Philip came home for lunch from Colaiste Eanna, the local secondary school he had started attending that September, a five-minute walk from his home at Ballyroan Road. Alice was rushing out because she was bringing Philip's sister to a dentist in the city centre, and so left the house before he started back for school. That was the last time she saw him.

"When I got home around seven o'clock that evening one of the girls met me at the door to tell me Philip hadn't arrived home, " she recalled. "Immediately I was a bit worried, because that was quite unusual for Philip. He was always home on time, around four o'clock. I went straight over to his friend's house to see if he was there."

Philip's friend hadn't seen him that afternoon in school and his father, a local garda, began calling around the hospitals. By this stage, the evening had turned dark, wet and windy. Alice got more and more anxious.

"I kept telling myself that he might have met some other children, or gone to the library or was playing football. But by that night I knew it couldn't be any of those things."

Philip didn't come home that night. His parents waited up and his brother and sisters sat together upstairs, while gardai started their search. By the following evening, Philip's picture was all over the television as a missing person, and milkmen around Dublin were handing out leaflets carrying his description.

For his family, the wait seemed interminable.

But when, six days later, Philip's schoolbag was found in a lane near his home, it brought no relief. The only clues, if they could be called clues, were that two of his religion books and one geography book were missing from it.

"All I could think of then was that someone else must have been involved, " said Alice. "Not that we ever thought that Philip had gone off of his own accord, but finding that bag really brought it home. That was very difficult."

It was also difficult for the Cairns family to be thrust into the public eye while trying to deal with Philip's disappearance. A "normal family, like any other on the street, " they had never had any dealings with gardai before. And this kind of case was new to the gardai . . . it was unusual for a child to go missing in such baffling circumstances. Mary Boyle, the seven-year-old girl who disappeared in Donegal in 1977, had been the last such case in the country.

"Everyone in the community was so good to us . . . the parish priest, Philip's teachers, all our neighbours, " said Alice. "No one could believe that something like that could happen in the community. But then, nothing like that has ever happened since."

Following the discovery of Philip's bag, his fellow students voluntarily went into school on their mid-term break to talk to gardai. Yet no clue to his disappearance was ever found, nor have there been any leads since. The 13-year-old boy who loved fishing, football and hurling had vanished.

"Day turned into night and night to day. Then years passed, " said Alice. "There was never any word." The past 20 years have been "extremely difficult, " she said. "But you still have to have hope. I never think of Philip as dead. I have no reason to believe he's dead. All I can do is hope I'll see him again and try and know that it's in the hands of the Lord."

Life has gone on for the Cairns family, with several weddings and two grandchildren, who live in Sweden, born into the family. On the 20th anniversary of Philip's disappearance last week, his brother Eoin described the pain of growing up without his big brother.

"He was my best friend, " he said. "Philip is always there in the sense that he is not there. At Christmas, birthdays, weddings and other family occasions we think of how Philip should be with us."

Once again, Philip's schoolbag is the centre of police attention, as gardai in Rathfarnham have expressed hope that advances in DNA technology will eventually be able to identify different people who handled the bag.

"The person may have been a child who found the bag elsewhere. That child is now an adult and perhaps has a family of their own, " said detective sergeant Tom Doyle. "Or the bag may have been found by an adult at some location and brought to the laneway. We need to find out where they found the schoolbag."

For Alice Cairns, it is a matter of continuing to hope that someone, somewhere comes forward with more information. "We know that someone out there knows more than we do, " she said. "I just hope they have the courage to come forward. It's been hard on the whole family. We're still able to function and keep going, but it's not easy. Nothing has been easy since Philip disappeared."