A child, aged 5, would have been violated in a nursery school in Ivry-sur-Seine, in Val-de-Marne.
It is the father of the student who filed the complaint on Thursday evening.
According to the dad, his 5 year old son would have asked to go to the toilet on Thursday and he would have been joined by an employee of restoration that would have violated.
His mother would have noticed traces of blood, the same night during the bath.
A man has been arrested and placed in custody on Saturday, before being exonerated and released.
The Safety region of the Val-de-Marne has been in charge of the investigation.