Tragic Julian Mynott, 42, and three-year-old Freddie died when their craft went over a 10ft weir just yards from their home.
Julian’s two other children, Archie, seven, and Florence, six, were rescued from a river swollen with floodwater and taken to hospital.
The dad — said by his own father to “idolise” the children — had bought the boat just days earlier as a treat for them and they were believed to be making their first trip.
Locals saw him struggling to reach the children after the boat capsized amid fast-flowing currents on the River Avon at Barford, Warwicks.
Julian and wife Emma, 41, who was not in the boat, had moved to the village only three months ago.
Grieving ... villagers leaving flowers yesterday
It is thought the antiques dealer was unfamiliar with the perils of the river, which runs past the boundary of the family’s imposing property.
One villager said: “The boat had gone straight over the weir. We could see the father in the water trying to swim towards his son but the current was too strong.”
A local waded into the water and grabbed Archie while a man and his girlfriend on the opposite bank threw across a life ring on a rope.
The couple hauled the ring back and got Archie ashore — then realised Florence had her foot tangled in the rope and had been pulled across the river upside down.
New home ... family's house
The man said: “One of the neighbours started performing CPR on her and my girlfriend sat with the little boy and gave him a blanket.” Last night Florence, who suffered cardiac arrest, was in a serious condition in Birmingham Children’s Hospital.
Archie was recovering in Warwick Hospital.
Police divers searched the river after the accident at 5.30pm on Saturday. They found the bodies of Julian and Freddie six hours later.
Julian’s sister Stephanie Skudder last night paid tribute to her brother, calling him “the best father in the world”.
She said: “My sister-in-law is going through hell, she’s lost her baby, her husband and her other daughter is critically ill.
“Julian loved his kids. He would not have left the river until he found his son.”
Julian ran an antiques business passed on to him by his widower father Roger, 69.
Roger, who now lives in Thailand and is on his way back to Britain, said: “Julian just idolised his children, he did everything for them.”
Yesterday locals tossed flowers into the river. Julian’s niece Sally, 19, wrote on Twitter: “RIP Ju and little Freddie. Love always xxxxxxxxxx.”
Police described the tragedy as “an awful afternoon”.