In a video the Hart of Dixie alum posted to Instagram Tuesday, the 18-month-old little boy is all smiles in a Nike tracksuit as he toddles from one end of the room to another, amid cheers and claps from people gathered in the room.
“And so as the rivers flow — commence the first steps,” King, 37, captioned the memorable moment. “Leo Thames #milestones (and on the day of the #womensmarch).”
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King — who is also mom to son James Knight, 3, with husband Kyle Newman — is at the Park City, Utah, festival to support her new film Bitch, in which she stars alongside Jason Ritter and Marianna Palka.
And little Leo Thames has come a long way. He underwent major heart surgery early in his life — something King described as “terrifying, and traumatic for us as parents, for our family.”
“Only a few of our best friends knew. I felt that I had to protect him in fear of the unknown, fear he would not make it. We felt isolated & confused,” the actress wrote on Instagram in August.
The caption was presented alongside an image of a letter from Cedars-Sinai Medical Center in Los Angeles, alerting King of a donation made to the hospital in honor of Leo Thames, from his godmother Taylor Swift.
“Our gift back is to share our story that anyone that is going through this is not alone, we understand & want to stand up to bring awareness in the greatest way possible,” King continued in the caption, while thanking her friend for her generosity and support.
“Leo Thames is the strongest, healthiest boy because of this team. He will live a full and whole life & never have to look back.”
In September, King shared with PEOPLE that her son was “doing amazing” since the surgery and she felt compelled to share her family’s story.
“I have a voice and I want to use that voice on behalf of my son — and I know that my son would want that,” the actress and designer added at the time. “He’s so strong. He’s such a fighter. He’s unbelievable.”