Senior Superintendent Raul Sandoval says the children, aged from 2 to 4, died before reaching a hospital, while their 32-year-old mother died while being treated.
He says the woman, Janeth Ponce, left a suicide note in her one-room shack in northern Laguna province's Magdalena township. She asked relatives to forgive her and care for her 7-year-old son who was sleeping in his grandmother's house at the time of the incident.
Police say her husband, a construction worker in Manila, had not sent money for a month.
One third of 90 million Filipinos lives below the poverty line of $1 a day.