The unnamed woman, reported to be from Mexico, was arrested late on Monday night following the boy’s death at their home in Alcamo, north-west Sicily, Rai News reported.
She reportedly told police that she went to wake her son yesterday morning, only to find that he had died in his sleep.
While the mother said she believed the boy had taken her anti-depression medication by mistake, police now think that she may have administered the drugs to her son, Rai News said.
In searching the family home investigators also reportedly found a letter, written by the woman, in which she talks about the boy’s death.
Neighbours described the mother as a calm woman who appeared close to her son, but that she was in financial hardship and relying on support from social services and the parish church.
The boy’s father moved to Germany following the couple’s separation and is due back in Italy on Wednesday. He had been reported for abusing the boy’s mother when they were together, Rai News said.