The parents of stylist Michelle Fournier and her 8-year-old son filed the civil lawsuit in Orange County Superior Court in Santa Ana.
The case seeks unspecified damages from the boy's father, Scott Dekraai, who is charged with eight counts of murder and one count of attempted murder in the Oct. 12 shootings at Salon Meritage.
Dekraai, who was immersed in a custody dispute with Fournier over the boy, is being held without bail.
The suit filed by Joseph and Geraldine Burke, who live in Batavia, N.Y., aims to obtain funds to help pay for the boy's expenses and college education, said plaintiffs' attorney Eric Traut.
It also seeks to cover funeral and burial expenses for Fournier, a 48-year-old stylist at the salon who was one of nine people gunned down during the rampage. Only one survived.
"He was clearly aware of the consequences of his actions, which included robbing his 8 year old of a loving and caring mother, and leaving an extended family with an indelible void in each of their lives forever," the lawsuit said.
Traut said he believes Dekraai has roughly $1 million in assets, including a home in Huntington Beach and property interests in nearby Seal Beach. He also receives disability payments for injuries he suffered in a 2007 tugboat accident.
Traut said he expects other victims will likely file similar lawsuits.
Dekraai, 42, is expected to be arraigned on the criminal charges Nov. 29.
A message was left Friday with defense attorney Scott Sanders.
Prosecutors are seeking the death penalty for the bloody rampage that rocked the tight-knit seaside community of Seal Beach. Orange County District Attorney Tony Rackauckas said he would not be surprised to see an insanity defense after an attorney for Dekraai asked a judge to ensure his client was receiving antipsychotic medication in jail.
According to paperwork filed by police in support of a search warrant, Dekraai told an investigator that he shot up the salon after arguing with Fournier by phone that morning. He took three handguns and donned a bulletproof vest and drove to a nearby beach where he thought about shooting his ex-wife before heading to the salon, according to the papers filed in Orange County Superior Court.
Dekraai shot eight people inside the salon, killing seven of them, then went outside and shot to death a man who was sitting in his car in the parking lot, prosecutors said.
Dekraai told police he fired at some people in the salon as "collateral damage" and believed the man in his car was an undercover or off duty police officer reaching for a weapon, the court papers said.