One of the two children recovered from the water had suffered a cardiac arrest and was given CPR by the resident and the policeman before paramedics arrived.
The youngster, whose age and gender have not been released, was taken to Warwick Hospital by land ambulance and was seriously ill, the West Midlands Ambulance Service (WMAS) spokesman said.
The second child was also taken to Warwick Hospital, conscious, but poorly," he said. "Shortly before 9pm a third child had been recovered from the water."
He added that this child was alive when found.
Three children have been rescued from the River Avon after their boat capsized near the Barford area of Warwick, Warwickshire .
Emergency services are continuing to search for a missing adult.