Paramedics performed CPR and the boy was hospitalized. He was in critical condition Thursday, according to the San Diego County Sheriff's Department.
"At this time, we have no information that would lead us to believe this is anything other than a tragic accident with the child," he said.
Police said they don't see any connection between Zahau's death and the boy's injuries.
In between the boy's accident and the discovery of Zahau's body, neighbors told KGTV, a loud party took place at the mansion on Tuesday night. However, police said Thursday they were not aware of any parties.
Coronado, a community of about 24,000 on a peninsula in San Diego Bay, had one murder last year according to the Associated Press.
Zahau, who previously went by the last name Nalepa, reinstated her maiden name, Zahau, in May, documents from the Superior Court of Arizona show.
Property records show Zahau's last known address was in Scottsdale, Ariz.
Investigating the Mysterious Death at the Spreckels Mansion
The mansion overlooking the beach is on the same block as the Larry Lawrence mansion, where Bill Clinton took his first vacation as president.
It was built by John Spreckels, a well-known California businessman who made a fortune in the shipping industry, eventually acquiring several properties, newspapers and the San Diego street railway system.
The home is more than 12,000 square feet and, according to KGTV, it sold in March 2007 for $13 million.
Curran said Thursday there is "no information indicating this is anything more than an isolated incident in the city of Coronado."