A traffic officer out on patrol first noticed the woman around 10:30 p.m. PT Thursday, when he saw the 43-year-old drinking alcohol in the passenger seat of the parked car.
After peering in to take a closer look, the officer found the woman was drinking with a 39-year-old man, who was sitting in the driver's seat while her son sat on the back seat.
Cpl. Richard De Jong of the North Vancouver RCMP said both the woman and man were highly intoxicated.
"Both adults were arrested for being drunk in a public place and lodged in police cells until sober," he said.
"This is a very disturbing incident for all involved, especially the three year old who is the son of the passenger."
Police said neither of the pair were sober enough to care for the woman's three-year-old son and provincial authorities were called out to take custody of the child.
The man, who was driving, also failed the roadside alcohol screening test and was issued a 90-day driving prohibition.