“I had no idea that this could happen,” Cassini says. “You think about sunburns and dehydration and all the things that can happen in the water, but I never considered cold shock.”

She says that Declan has made a full recovery.

Water below 70°F can cause hypothermia even on a balmy day, according to Dr. Christopher Kelly, chief of pediatric emergency medicine at NewYork-Presbyterian Brooklyn Methodist Hospital.

“Temperatures drop relatively quickly in kids, so that puts them at a higher risk for hypothermia,” Kelly, who did not treat Declan, tells TODAY.com. “As their temperature drops lower and lower, they start to get a little confused, and you might notice some slurred speech.”

If you suspect your child is experiencing signs and symptoms hypothermia, Kelly says to seek medical care immediately. It’s important to rule out other causes such as low blood sugar.

“You want to dry them off with warm — or at least dry — towels,” he says. “And you want to keep their heads covered because kids lose a lot of heat from the top of their heads. Other than, it’s really just kind of that gentle warming until their body temperature comes up.”

To prevent hypothermia, Kelly says to pull your child out of cold water for periodic breaks — even if they insist they’re fine.

“Kids just want to have fun and don’t care if they’re cold,” he says.

Cassini’s Facebook posted has been shared 12,000 times.

“This exact same thing happened to my son on a beach in Maine a few years ago. Thankfully there were a lot of nurses on the beach that day but we ended up going to the ER just to be sure. Thank goodness your son is ok. They bounce back so quick. Us moms…..not so much,” one person wrote.

Added another, “This same thing happened to me when I was 10 years old. It was super scary for me and all involved. I’m very glad your little boy is okay. And thank you for sharing your story so more parents and caregivers can learn from your experience.”