London, May 3 : The impact of monster Josef Fritzl has been so dreadful on the kids he fathered with his daughter that according to psychiatrists they could face up to eight years of intensive therapy.
According to Professor Max Friedrich, the Fritzl's children are afraid of the colour blue, birdsong and rustling leaves.
He believes that it will take a long time for them to recover.
"It will take them between four and eight years of intensive therapy," The Daily Express quoted him, as saying.
The extent of the damage to Stefan, 18, and five-year-old Felix is just becoming clear.
A windowless chamber has been built for when they need to retreat.
But Bernhard Kepplinger, the supervising doctor for the Fritzl family, including the three children raised above ground, is more cautious.
"Each child will need individual therapy and we should be careful not to overdo it," he said.
An immediate task is separating Stefan and Felix from their traumatised mother Elisabeth, 42.
"They were probably overprotected in the cellar," said Dr Kepplinger.
Elisabeth spent 24 years locked in the dungeon under Fritzl's house in Amstetten and had to shield her children from the father's sexual abuse.
According to sources on the investigation team, when they heard their father raping their mother they would retreat to a bedroom and watch TV to block out the noise.