The pair, a 45-year-old man and a six-year-old boy, died within hours of being trapped in the sunken boat for 20 minutes on Saturday night near the French capital’s Notre Dame cathedral, hospital officials said.
Their identity was not given but the man was not the boy’s father as had been assumed earlier.
Police said the private boat had “gone straight down”. They did not know its name or who owned it.
Ten of the 12 people on board — six adults and six children, all of them French and from six families — had been plucked from the water after the boat sank.
Hospital officials said five children between three and 14 and five adults aged 38 to 45 were slightly injured.
Swirling currents at the scene of the accident where the river narrows as it flows around the island on which the cathedral sits complicated rescue operations, firefighter Joel Prieur told the press.
The exact cause of the accident is still unclear.