The last snatched phonecall came on Saturday as Fatima used a mobile phone to ring home, telling her father: "Papa, they are beating me, they are beating me." Moments later, the line abruptly went dead.
Speaking to the Irish Independent from his home in Firhouse, south Dublin, Mr Halawa, imam of the Islamic Cultural Centre in Clonskeagh, said he had urgent fears for his children's safety.
The siblings and their mother, Amina Mostafa, were on their annual holiday to Egypt when they were caught up in a protest that turned violent at Ramses Square in the centre of Cairo. Their distraught mother, who was not with the siblings at the time, is now making frantic efforts to get access to her children in custody.
"On Friday, I heard from my daughter (Omaima) in the square. She said a plane dropped a bomb on them on the street. They entered the mosque and they prayed in the mosque and when they went out to go home everything was closed," said Mr Halawa.
"From 7pm to 7am, everything is stopped in Cairo at night. The underground was closed, there were no taxis running. She entered the mosque and then the army and the policemen came."
Mr Halawa said the latest news he had heard was that his children were being held in Tora Prison.
"They are in Tora in Cairo. A girl who was inside -- and she got out because her uncle is a big man in the police -- she was with them in the mosque. She said my daughters and my son were inside the prison with them. I phoned the Department of Foreign Affairs this morning and they told us they will meet them. I hope soon," he added.
"My wife is very worried. I'd like to see what I can do here before I go to Cairo next week."
The Department of Foreign Affairs said it was in "ongoing contact" with the Halawa family and the Egyptian authorities. Irish Ambassador to Egypt, Isolde Moylan, is leading the consular efforts.
Last week, the department updated its travel advice for Egypt, saying a state of emergency had been declared. In July, due to the ongoing civil unrest, it advised against non-essential travel to Egypt, except for the Red Sea resorts.