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World Premature Day was Thursday, and it hit especially close to home for Chris Pratt.

The actor and his wife, Anna Faris, welcomed their now 4-year-old son Jack into the world as a preemie. Though he was only three pounds at the time, he's now grown up to become a perfectly healthy and happy little boy.

In fact, Pratt took to Instagram to share a precious video of his son, playing with a Praying Mantis. 

"As many of you may know, our son Jack was just over 3 pounds when he was born," the proud dad wrote. "Thanks to scientific advances made possible by #marchofdimes funding, today he's a perfectly healthy, curious 4 year old."

Chris Pratt, Jack Pratt

Suzi Pratt/WireImage

Pratt has been a big supporter for March of Dimes since his son's premature birth, always speaking out about the experience.

In 2014, he gave an emotional speech during a luncheon for the foundation in 2014, saying, "I've done all kinds of cool things as an actor: I've jumped out of helicopters and done some daring stunts and played baseball in a professional stadium, but none of it means anything compared to being somebody's daddy."

He recalled holding his tiny son in the NICU after his birth. "I made promises in that moment about what kind of dad I wanted to be and I just prayed that he'd live long enough that I could keep them," he said.

And look at him now! "Our Jack went from a small, helpless little squirt to a strong, smart, happy, funny, beautiful boy who loves monster trucks and Daniel Tiger, and, believe it or not, loves vegetables," Pratt noted. "Broccoli and cherry tomatoes are his favorite foods."

All of this, he said was due in part to the March of Dimes.

"None of what we went through would be as easy even 10 years ago," the actor told the crowd at the time, adding that the NICU hangs on a balance of life or death. "A balance that's tipping towards life by cutting-edge medicines, much of which is a direct result of this wonderful organization, the March of Dimes."