The manager of the park in the town of Akyazi and his son jumped into the water in an effort to save the children, who were caught in an electrical current, the private Dogan news agency reported.
But the men also became trapped in the current and were electrocuted.
It was not immediately clear what had caused the tragedy but the state-run Anadolu news agency reported a probe had been launched.
Hasan Akcan, Akyazi's mayor, said the park had received a license in 2012 as a swimming pool and amusement centre, adding that what happened was "saddening," according to Anadolu.
