The lawyer for Stanley and Julia Patz, Brian O'Dwyer, tells the News, "The point is to establish once and for all that Ramos is responsible for Etan's death."
The suit could also unearth some information that help lead to criminal charges against Ramos, O'Dwyer says.
The Daily News reports Ramos was the boyfriend of Etan's babysitter on May 25, 1979, the day the 6-year-old disappeared on his two-block walk to his school bus in downtown New York City.
Former federal prosecutor Stuart GraBois, who worked on the Patz case, says Ramos has admitted taking Etan to his apartment, but denied killing the child.
However, a CBS News investigation reveals that at least two inmates independently claim that Ramos told them details about Etan's disappearance.
Manhattan prosecutors recently reopened the case, removing ash, dirt, and a coal-fired furnace from the basement floor of Ramos' old apartment building in August.
Ramos, serving 10 to 20 years for sexually abusing two boys in Pennsylvania, was denied parole in June. His sentence runs until 2014.