The abuses were allegedly committed against a dozen hungry, vulnerable children at a displaced persons camp at M'Poko International Airport in Bangui, the capital of the Central African Republic, between December 2013 and June.
In its statement, the Paris prosecutor's office announced "a judicial investigation against unnamed persons accused of charges of rapes on minors" aged under 15 years, or complicity in this, "by people abusing the authority conferred by their functions."
Investigating magistrates will now continue the investigation, it said. It did not state how many soldiers were under suspicion.
According to the Paris prosecutor's office, it was sent a confidential U.N. document by the French Ministry of Defense in July reporting the testimonies of six children ages 9, 11 and 13 about abuses at the M'Poko camp.
Four of the children said they were victims of sexual abuse by peacekeepers with France's Operation Sangaris, and two said they had witnessed abuse.
On receiving the document, the military affairs section of the Paris prosecutor's office immediately launched a preliminary investigation, its statement said, and sent investigators to the Central African Republic for a week in August. They carried out a number of interviews but have not yet interviewed any children in connection with the allegations.
The Paris prosecutor wanted to speak beforehand with the U.N. official who wrote the report, the statement said, and she agreed to come to Paris.
"The U.N. hierarchy, however, refused this hearing, indicating that the official benefited from an immunity that had to be lifted before any hearing," the statement said.
Eventually it was agreed that the official could complete a written questionnaire, which was returned to the Paris prosecutor's office last week, it said.
The director of an advocacy group that was sent a copy of the leaked U.N. report told CNN last week that French soldiers forced hungry, homeless young boys to perform sex acts on them in return for small amounts of food, water and sometimes some cash.
"The children were severely traumatized by the events," said Paula Donovan, co-director of AIDS-Free World.
Hollande promises heavy sanctions
A French Defense Ministry spokesman told a news conference in Paris last week that the army had not gone public about the case previously because a judicial inquiry was ongoing.
In response to the furor, French President Francois Hollande promised heavy sanctions against any soldier found guilty of the allegations.
The United Nations confirmed it had suspended a staffer over the leak of the document last summer to the French government.
The unnamed staffer is accused of providing an unedited version of the internal U.N. report to French authorities before it even reached senior management in the U.N. Office of the High Commissioner for Human Rights.