Two toddlers drowned Saturday in a pond outside their Long Island apartment after their mother fell asleep inside, according to police and police sources.

The tragedy unfolded behind the Fairfield Townhouses in Holtsville around 3:15 p.m., Suffolk County police said.

Sources told The Post that the girls slipped out of their home while their mother slept.

The sisters snuck out of the apartment while their mother was sleeping, sources said. GoogleMaps

The bodies of the sisters, aged 2 and 4, were found in the water by a search team just minutes after a family member reported the girls missing.

They were rushed to Stony Brook University Hospital where they were pronounced dead, cops said.

It is not clear how long the girls were in the water before they were recovered.

The toddlers were found unresponsive in the pond just minutes after they were reported missing. GoogleMaps

The Fairfield Townhouses, located south of the Long Island Expressway, touts its “expansive grounds with pond and walk path” on its website.

One and two-bedroom units range from $2,475 to $2,900 per month.

A message left for the management office was not returned.

Police are investigating the incident and are asking those with information to call its homicide tip line.