Wallington Fire Department Rescue Co. 204 said they are performing a water search in the Passaic River with their marine units.
Around 6:21 p.m., officials received reports of children going into the river near the off-ramp in the park.
Passaic Mayor Hector Lora said a girl was accounted for and out of the water with her parents but two other children, a 10-year-old boy and girl are still missing.
The mayor said boats and drones are all over the river searching for the children.
"Any parent would be there extremely concerned, but we are holding out with hope. We are praying. We have faith. Our police officers, our firefighters are doing everything that they can to locate these children. Again, there were three that went into the water. We have that confirmed. There's one that came out," Lora said.
Lora said a man in the park jumped into the water to try and save them but when he was about five meters deep, it was too deep and the current pushed him away and he could not reach them.
The 11-year-old girl who managed to get out of the river on her own is the sister of the boy who is still missing. The other girl who is missing is their friend, the mayor said.
"She expressed that they were in the water they were trying to get out she got out at a different point not too far from here - she is back with her mother and she's worried about her brother as well as the friend that was with them," Lora said.
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