A person, who said they were a train driver, posted to the Rakaia Community Noticeboard about the children playing "chicken" with the train at a pedestrian crossing near the dog park.
The post included a photo from the front driver compartment, looking out onto the train tracks.
It followed a post earlier in the month from a woman in the group concerned about the same issue.
Senior Constable Trevor Gurney, of Rakaia, said no one had reported the behaviour to him.
However, he had become aware of three children playing on the tracks through other sources.
"I have found out who it is and I’m dealing with it," Gurney said.
He said he was talking to the parents to ensure it did not happen again.
He advised anyone who witnessed dangerous behaviour such as this to report it to police in the first instance, rather than post about it on social media.
"We just want kids to be safe at the end of the day," he said.
The train driver said in the post they would see the children after coming around a bend, travelling south after exiting the Rakaia bridge. They were concerned about running the children over.
"If you know who these kids are that play around there please, give them a what’s up from me, because all it will take is for one of them to get their shoe stuck in the track at the crossing to ruin a family’s and my life," they said.
"All I can do is hang off the horn to make them get off the track."
