Gardai have raided five addresses and seized computers as part of an international operation to break up an internet child-sex network.
Officers are running forensic tests on the computers that were seized in July and August as part of "Operation Koala".
The investigation began after a video of a child being sexually abused was found in Australia last year.
The trail lead the European police agency Europol to an Italian national (42) who ran a website selling sexually explicit videos of underage girls to around 2,500 customers worldwide.
Police said the man sold over 150 self-made videos of underage girls and took thousands of photographs over the 18 months that he ran the business.
Police said the videos were mainly produced in Ukraine and included a father sexually abusing his daughters aged nine and 11.
Max-Peter Ratzel, Europol's Director, said 23 children aged between nine and 16 years of age have been identified in the massive investigation ongoing since last year.
"This successful investigation has been extremely time-consuming, but the fact that the perpetrators behind these outrageous assaults towards children now are facing justice makes every hour used worth it," he said.
Operation Koala was sparked last year after a child abuse video that had been produced in Belgium was discovered in Australia.