On Monday, Travolta, 66, shared a photo on Instagram that wished his son a happy birthday.
The photo was a black-and-white one, featuring Travolta and Jett smiling at one another while embracing.
"Happy Birthday Jetty! We love you!" wrote the "Grease" star in the caption, adding a red heart emoji.
Preston, 57, also took to Instagram on Monday, sharing a photo of herself and Jett, also hugging and smiling.
"Happy Birthday to our sweetest Jetty, we love you!!" read the caption.
A third birthday wish came from Travolta and Preston's daughter Ella.
"Happy Birthday to my brother Jett," she wrote in the caption of a throwback photo featuring the whole family. "I love you so much."
In the days leading up to Jett's birthday, Preston shared a message of support on Instagram for those with autism, like Jett.
The "Jerry Maguire" actress shared a throwback photo of her family, featuring Jett smiling at his father.
"I have a special place in my heart for those with autism and special needs. Sending love to some of my favorite people in the world," read the caption. "My son Jetty was one of the most playful and wonderful souls you’ve ever met. Love to all of you with autism and special needs around the world."