Speaking to the media, Police Colonel Jen Fajardo said the victims were all from Quezon province, southeast of Manila.
According to a police report, the infant died of drowning after he was washed away by raging waters, while a male and a 14-year-old boy were pinned by fallen trees during sleeping at their respective homes.
The National Disaster Risk Reduction and Management Council (NDRRMC) has yet to report deaths from Ewiniar, the first typhoon to batter the Philippines this year.
However, the agency reported that at least seven people were injured in the Bicol region, southeast of Manila, due to the typhoon.
According to the NDRRMC, nearly 20,000 people in four regions have been affected by the typhoon. More than 2,000 displaced people have been living in government-run evacuation centres, while the rest stay with their relatives.
Quezon is one of the provinces hit hard by Ewiniar.
The Philippine State Weather Bureau PAGASA said Ewiniar maintained its strength on May 27 while moving northwestward over the Philippine Sea at 10 km per hour, with peak winds of 140 km per hour near the centre and gusts of up to 170 km per hour.
Ewiniar is expected to leave the Philippines by May 28 afternoon or evening.
The Philippines is one of the most disaster-prone countries globally. It experiences 20 typhoons yearly, some intense and destructive.