The Police Ombudsman has launched an investigation after children as young as four were searched during a major police security operation.
A group, comprising 12 children and nine adults, was returning to Belfast from a visit to Dublin's Kilmainham jail when the minibus they were travelling in was stopped on the A1 dual carriageway close to Banbridge shortly after 5pm on Sunday.
Police last night said four children were searched during the operation. However, this is disputed by parents who say all but one child on board the bus was searched. They also claim that one child wet himself during the search.
A senior member of the hardline Republican Network for Unity, Carl Reilly, was on the bus.
It is understood both children and adults were removed from the bus while they and the vehicle were searched during the operation.
Last night a solicitor acting for the children and their parents, Kevin Winters, said the PSNI could now face civil proceedings after the group was detained for almost two hours.
Mr Winters said legal action could follow the incident. He has reported the matter to the Children's Law Centre, Children's Commissioner and the Human Rights Commission.
Belfast woman Lisa Britton, who was on the bus with her two children, said they were traumatised by the incident.
She said: "It was horrifying, especially for the kids, and my wee girl who is four is totally traumatised. My nine-year-old son panics every time he sees a police Land Rover. The PSNI took videos of the adults and the children, even though we told them we didn't want that.
"I wanted to get someone to come along and take my children. I'm very angry about this."
A spokesman for the Police Ombudsman said: "We have received a complaint about the incident and are currently making further inquiries."
A spokeswoman for the PSNI said that children were among those searched last weekend. She added: "We will fully co-operate with the Ombudsman and welcome the oversight of this office."
A spokesman for the Children's Commissioner said: "We cannot discuss individual cases. We are aware of the incident."