According to video captured during the rescue, an officer can be heard shouting, "They are in the water! They are in the water!" before running toward the girls.
"Hold on! I got rope," the officer says as he throws a line to them. A third child, a boy, had already made it out of the water before first responders arrived.
Westampton Township Fire Chief Craig Farnsworth said the children were fortunate.
"They're very lucky," he said.
He added that "hypothermia will kick in pretty quickly. Your body starts to shut off blood to the core to try to protect the vital organs."
As Mount Holly police pulled the girls to shore, one could be heard crying, "Thank you! Thank you!"
Officials said the rescue reflects the type of emergency first responders regularly prepare for.
"They want to save people and help people and it's something that they practice and really work hard on," Westampton Township Mayor Sandy Henley said.
Drone footage showed the Westampton Fire Department conducting ice rescue training, which Farnsworth described as essential during colder months. He warned that "even when it's cold, over time the ice will also start to get thin over time. All ice is dangerous ice."
Farnsworth urged people never to walk on frozen bodies of water. If someone falls in, he said, they should "try to spread your weight out across the ice that hasn't fallen, kick as hard as you can, get yourself off and slowly crawl your way off the ice."
For bystanders, he advised, "call 911 as quickly as possible" and "get a stick or a long branch, try to throw it or get to them as quickly as possible."
The rope technique used by police mirrored the safety guidance, helping bring the girls out of the water.
All three children were taken to Virtua Hospital as a precaution and are expected to be OK. Westampton Firefighters later retrieved their backpacks from the lakeside.