French police is investigating the death of a 5-year-old, who likely died following a cardiac arrest in "suspicious circumstances".

His stepfather, identified only as 30-year-old Julien M in the French media, called the emergency services in the early hours of 6 February indicating the young boy had difficulties breathing. The boy's identity was at first not revealed by the investigators, but he has been named as Yanis in the local newspaper L'Echo de la Lys.

The investigators are still piecing together what happened exactly to the child, who was found near a canal in the small town of Aire-Sur-la-Lys, near Calais, France. His body, reportedly clothed only in wet underwear and socks, bore the traces of previous wounds, possibly resulting from past beatings. The police found him unconscious, and his face showed a broken nose.

"The investigation needs to determine whether the child died of cold, if it was the consequence of a fall, or a case of mistreatment," a policeman told Le Parisien.

According to the newspaper Le Parisien, the investigators believe the man had made the child run outside the house until he was exhausted as a punishment for wetting the bed. The boy's mother – a 22-year-old woman – and the man had no other children and were not previously known to the authorities.

The couple has been arrested. Speaking to the press, prosecutor Patrick Leleu explained there were sufficient elements to detain the parents. "The suspicious circumstances of this death led us to put the parents in custody on suspicion of manslaughter".