Prosecutors decided to open the investigation after written consultation with the author of a UN report that first raised the allegations, the prosecutors’ office said in a statement.
A preliminary investigation was opened last July based on the UN report.
That report detailed the alleged abuse from December 2013 to June 2014 at a centre for displaced people at M’Poko airport in the country’s capital Bangui.
The allegations came to light in April after an internal UN report summarising interviews with victims was leaked.
The report, a copy of which was seen by Reuters, suggests at least 13 French soldiers, two soldiers from Equatorial Guinea and three Chadian troops had been involved in the alleged abuse.
The six-page document said children who were interviewed alleged they had performed oral sex on the French troops. The soldiers from Equatorial Guinea and Chad were accused of sodomising children.
The Bangui public prosecutor Ghislain Grezenguet said local authorities had also opened an investigation after identifying a number of individuals.
France’s Defence Ministry said last night the findings of an internal military inquiry would also be declassified.
France intervened in its former colony about 18 months ago to stem violence between Christian militants and largely Muslim Seleka rebels. It started withdrawing some of its 2,000 troops this year, handing over to UN peacekeepers.
President François Hollande, a strong advocate of using the French military to secure peace in ex-colonies, has vowed no mercy if the allegations are proven.
The move hands the investigation to independent judges instead of the Paris prosecutor’s office, in an acknowledgement of the seriousness and complexity of the accusations, amid international dismay surrounding the case.
After the French defence ministry was informed of the rape accusations last summer, the Paris prosecutor opened a preliminary investigation.
The case was made public only last week, more than nine months later, following a report in the Guardian.