Autopsies of a 2-year-old girl and her 3-year-old brother who died in the Bronx early Monday revealed that they were beaten to death, and the police said they were investigating the case as a homicide.

The simultaneous deaths of the Bronx siblings — Olivia and Micah Gee — raised immediate suspicions among investigators, who were skeptical that they had died of natural causes after seeing bruising on their bodies, law enforcement officials said.

The children’s mother, Jade Spencer, 31, called 911 around 1 a.m. Monday after they were discovered not breathing and unresponsive in their apartment on Van Cortlandt Park South in Kingsbridge.

She informed the emergency workers that both toddlers had severe asthma, and they were rushed to Montefiore Medical Center, where Olivia died at 2:10 a.m. Micah died a few minutes later.