Preston posted a throwback photo on Instagram that captures a sweet family moment with son Jett, who died at 16 of a seizure in 2009.
"To my sweet love, Jett ... you are in our hearts forever,'' she wrote. "I send love to all of the beautiful autistic children and the wonderful people who love them. May we all shine and grant love and respect to children with special needs."
Travolta responded in the comments section of the post with a heart emoji.
Jett, who had a history of seizures, died from one while on vacation with Preston, 56, and Travolta, 65, at their home in Grand Bahama Island.
Police officials said he hit his head on the bathtub after suffering a seizure, though his body showed no sign of head trauma and his death certificate says he was killed by a seizure.
The couple had not spoken publicly about Jett's autism until revealing he had it after his death.
Travolta testified in a trial of two people accused of trying to blackmail him that Jett had autism and a seizure disorder. He also said he desperately tried to save his son by administering CPR after a nanny told him Jett had fallen ill.
The couple have a daughter, Ella Bleu, 19, and a son, Benjamin, 8, who was born nearly two years after Jett's death and helped Preston and Travolta move forward after losing Jett.
"Holding him for the first time was magical,'' Preston told People after Benjamin's birth.