Gerry and Kate McCann's son asked them whether they had covered up his sister Maddie's death after a former cop claimed this happened in a book, the libel trial has heard.
The McCanns spoke to reporters after delivering personal statements at Lisbon's Palace of Justice in the libel case brought by them against Goncalo Amaral.
They also said they fear their daughter Madeleine's kidnapper may "strike again" and believe that he or she will have been "laughing" at a former police officer's claims that they hid the girl's body.
He made claims in a book their role in the disappearance of their daughter from the family's holiday apartment in Praia da Luz in the Algarve in 2007.
He said Madeleine had died in their apartment and her parents hid the body to cover it up.
Answering questions from judge Maria Emilia Castro during the hearing, Mrs McCann said that her young son Sean had asked her about the allegations that she was involved in her daughter Madeleine's disappearance.
She told the court that Sean heard about Mr Amaral's allegations on the radio while travelling on the school bus.
"Sean asked me in October 'Mr Amaral said you hid Madeleine'. I just said that he said a lot of silly things," she said.
Sean and his twin sister Amelie were aged two when Madeleine, who was nearly four, went missing.
Mr McCann said that whoever was involved must have been laughing during these last six years at what Mr Amaral has claimed - that there was no abduction and there is no predator out there.
"There is - he or she or they may strike again," he said.
"There's an unsolved serious crime and there's a series of other crimes against children which have come to light who have been on holiday so at the very least these people need to be brought to justice.
"We don't know if Madeleine is alive or dead but there is no evidence that she is dead and she is a missing child and she is completely innocent."
The couple earlier told the court that there was no doubt that Mr Amaral's claims had done "severe damage" to their struggle to find Madeleine.
Mrs McCann said that the couple make efforts to keep information about the abduction away from their children.
"We try and anticipate if there is going to be any media coverage so they don't get any shocks and are prepared and confident to handle it," she told the court.
"It is very distressing to us as adults so for a child it would be very, very distressing."
She also told the court that the children were now old enough to use computers at school and home and had to be supervised.