Video shows little Anthony James Jackowski, now 18 months, stomping around his parents' living room with a massive smile on his face.
Known as AJ, one clip shows the mischievous tyke making his way out of his coloured playpen across the room to his milk bottle.
Then he taps his bottle against dad Anthony's coffee mug as mum Melissa, filming the adorable scene, says: "Cheers!"
First walking on December 3, at exactly 18 months old, AJ's first steps are massive strides for the 'medical marvel' who was born three months early.
Weighing just 1lb 13oz at birth, AJ survived three separate bouts of necrotising enterocolitis (NEC) and nine surgeries.
His parents Melissa, 41, and Anthony, 47, who previously struggled to conceive for 10 years prayed their boy would "fight his way through the pain".
Against the odds, AJ pulled through - and after 211 days in hospital, he's enjoying his first Christmas with his mum and dad at home.
Melissa and Anthony, who together run a cleaning company in Ebensburg, Pennsylvania, "thank God that AJ can get back to being a kid".
His mum described AJ, just under 19lb, as a "wild child" who "bashes his head as he walks" and "loves to keep moving and getting about".
AJ is "a fun, loving, intelligent, smart little boy" who is now "speaking and hasn't been held back developmentally" - Anthony said.
Tearful, both parents described his newfound passion for walking as "the perfect gift" and "a real Christmas miracle".
Melissa added: "We hoped and we prayed, and hoped some more that AJ would get through all this - and unbelievably, he did!
"Anthony and I never felt like we were the unluckiest parents in the world, despite having to wait 10 years to have our own child.
"We were just happy that he was in this world, and we so wanted him to pull through.
"The whole time, we've rooted for him, and we've been by his side 24/7.
"And amazingly, he's a little fighter - he fought his way through everything, and struggled through, and he's still with us!
"His will to live is unbelievable, he so wanted to be around!
"AJ is not like most children - it's basically unheard of to survive even necrotising enterocolitis once, so to do so three times is crazy!
"We're so grateful and blessed, we truly believe in the magic of Christmas!"
Melissa and Anthony struggled to conceive for nearly a decade after getting married in 2009 - and were resigned to being "just an aunt and uncle".
They discovered that Melissa was pregnant with AJ on New Year's Day in 2018 - and took 11 pregnancy tests just to make sure.
All the results came back positive.
"We already felt blessed, just by being pregnant," Melissa revealed.
"Everything else that followed should have knocked us back, but it never did - it made us feel even luckier that there was someone to look after."
After undergoing a c-section on June 3 in Conemaugh Valley Memorial Hospital, AJ and his parents were rushed to UPMC Children's Hospital of Pittsburgh.
Born over 14 weeks early, weighing 1lb 13oz, tiny AJ was just 12in long.
"He could fit in his dada's palm," Melissa said.
Diagnosed with NEC, a condition where a portion of the bowel dies, AJ spent the next 211 days in the neonatal intensive care unit (NICU).
He was then diagnosed a further two times with NEC after displaying symptoms including skin discolouration, and infections caused by the disease.
AJ underwent a whopping nine surgeries between June and December 2018 - and finally came home on December 30.
Starting from last January , AJ has been nursed at home every day, and received physical and occupational therapy once a week.
Despite suffering a nasty bleed on the brain at birth, he is speaking, and will soon receive speech therapy as well.
This is AJ's first Christmas outside of the children's hospital - but Melissa and Anthony won't be taking him out and about.
"Because of AJ's weakened immune system, we isolate during flu season so we will be home as a family," Melissa said.
She and Anthony, though, said that AJ can expect lots of goodies from Santa Claus this year - including books, toys, and an Elmo potty!
And when AJ took his first steps, Melissa and Anthony "burst into tears".
Melissa bravely revealed: "We feel like we've experienced a miracle - every wish we had while AJ was in hospital has come true.
"We couldn't despair, because he hadn't given up.
"AJ is home for his first of many Christmasses - to be honest, we have everything we could want for this Christmas, and more!"