A policeman has told how two children kept prisoner in an Austrian cellar for their entire lives were "open-mouthed with awe" when shown the outside world for the first time.

Five year old Felix and his brother Stefan, 18, were kept locked in the cellar of a house in the town of Amstetten by the man who was both their father and grandfather, Josef Fritzl.

Neither boy had seen daylight before, their only experience of the outside world was what they saw on television whilst imprisoned along with their sister Kerstin, 19, and mother Elisabeth.

Fritzl kept Elisabeth, his daughter, locked in the basement for 24 years while repeatedly raping her - forcing her to have seven of his children. One of the children, a twin, died as a baby and was incinerated by Fritzl.

The other three children were brought up by Fritzl and his wife as foster children in the family home. His wife claims to have no knowledge of the secret cellar and says she believed their daughter had run away, later returning to leave the children on their doorstep.

Kerstin, the eldest of the children kept in the cellar, is now seriously ill in intensive care. It was her need for medical treatment that eventually led to the family's discovery.

Police have described in detail the first moments of freedom for the boys.

Chief Inspector Leopold Etz said: "This was the first time they had been out in the real world in their lives.

"Everything was new and it was clear they were amazed. The only idea they had of the real world was what they'd seen on television.

"It was their first car ride ever, and they were amazed at the speed and really excited. They had never known anything like it. They had only ever seen cars from the TV.

"The best bit was when they saw the moon. They were just open-mouthed with awe, and were nudging each other and pointing. They had never even seen the moon."

"Travelling in one was a totally different experience, especially for Felix who was beside himself with excitement.

"He was shrieking with pleasure when he saw cars coming the other way, and he and his brother braced themselves whenever a car went past. They thought there was going to be a head-on crash.

"When we left the hospital with the boys it was dark, and they were fascinated by the headlights. They were shouting and hiding behind the seats.

"The best bit though was when they saw the moon. They were just open-mouthed with awe, and were nudging each other and pointing. They had never even seen the moon.

"In all my years as a policeman I have seen a lot, but I have never seen anything like this. "

The two boys and their mother are being kept in a special unit and are receiving both medical and psychological treatment.

Josef Fritzl has been remanded in custody and faces up to 15 years in prison if he is convicted of raping and beating his daughter.

Police are also considering charges of "murder through failure to act" in connection with the death of one of the seven children he fathered.

Meanwhile, hundreds of people in Amstetten took part in a candlelit vigil in the town's main square to show their support for Fritzl's victims.