The UN mission in Haiti had requested an immediate investigation by the Office of Internal Oversight Services (OIOS), a UN internal watchdog.
Montas said: "All accused Sri Lankan battalion members will be repatriated on disciplinary grounds on Saturday, November 3."
The Sri Lankan military has said the soldiers could face severe punishment if they are found guilty.
Brigadier Udaya Nanayakkara, a military spokesman, said: "If they are proved guilty, the maximum punishment will be given according to the Sri Lankan law and military law."
Under Sri Lankan law, hard labour is the maximum punishment for such offences.
Montas said that it was up to Sri Lanka to deal with the allegations.
"They are back under national jurisdiction. So far, Sri Lanka has said ... that they are going to be prosecuted in Sri Lanka," she said.
As peacekeeping missions have expanded in recent years, reports of abuse have spread despite the UN's declared "zero-tolerance" policy towards misconduct.
More than 800 UN troops were recently suspended amid claims of commiting sex abuse in Ivory Coast.
A report published in 2005 said UN soldiers should be punished for any sexual abuse, have their pay docked and a fund should be set up to assist any women and girls they impregnated.
But member nations have not agreed.