Yumiko Takahashi knew that 19-month-old Neo was running a high fever when she checked on him on the afternoon of June 24 last year but left him lying on his bed untended, police said.

A post mortem examination revealed Neo had died around 2 pm on June 26th, police said. His mother found his lifeless body the following morning, newspaper reports said.

Takahashi, 29, was arrested Thursday on suspicion of child neglect and causing death, a spokesman for police in Otsu, western Japan said Friday, adding that the lag had been due to officers "carrying out the necessary investigations".

Takahashi, whose first child died a few days after birth and who lost another son in a fall from an apartment balcony, told police she had been using chatrooms, media reported.

"I have sought solace in chatting on the Internet to get connected to other people for three years since I got depressed for losing my son in an accident," broadcaster NHK quoted her as saying.