It said it found “graves of child or infant size” at an area on the western edge of the site, where excavations have been carried out under a tent.
It corresponded to an area labelled as “burial ground” on historical maps of the site.
ODAIT said: “Despite these historical references, there were no surface or ground level indications of the potential for a burial ground at this location prior to excavation.
“The presence of burials at this location has now been confirmed.
“The layout and size of the graves is consistent evidence that, at this part of the site, there is a burial ground from the time of the operation of the mother-and-baby institution.”
The institution was open from 1925 until 1961.
ODAIT said it recovered four more sets of human remains in the same area, further to the seven which it had found in its previous update last month.
It said “initial assessments” indicated that all eleven remains were of infants and they had been in coffins.
Further analysis is being carried out on the remains.
The excavations under the tent are being carried out by machine and by hand.
The area is about 100m from another part of the site where investigators from a government inquiry found “significant quantities” of remains in underground chambers in 2017.
The Director of Authorised Intervention, Daniel MacSweeney, is leading the team.
He has previously worked for the International Committee of the Red Cross in operations to recover missing people.
He told the Irish national broadcaster RTÉ that the confirmation that infant remains were present was “very important”.
Mr MacSweeney said that 160 people had made contact with a view to giving DNA samples to help identify the bodies.
He expressed hope that more would now follow, saying: “I know from experience that sometimes the discovery of remains can be a catalyst for people to come forward.”
