What happens next is up to investigating judges in France, but as no one has been charged a trial appears unlikely.
France opened a first probe into the child rape allegations in 2014 concerning French soldiers deployed in Central African Republic to restore security after months of violence between rebels and militia fighters.
The prosecutor believes sexual abuse may have occurred during the 2013-2014 deployment but "differences in the testimonies" meant it was not possible to establish guilt among the French troops, a source close to the case told French news agency AFP.
British daily The Guardian first revealed the accusations to the public in April 2015, reporting that six children aged between nine and 13 had said they were abused in a camp for displaced people in CAR's capital Bangui.
Since then, other reports have emerged about troops' alleged involvement in sexual attacks and giving children food and sometimes small amounts of money for sexual services.
Six French soldiers were questioned but none were charged and all denied committing any sexual abuse.