A rescue crew was sent to the 40m (131ft) tall Vilyuchinsky waterfall in the Kamchatka peninsula after four people became trapped on Thursday.
All were pulled from the ice, and a boy and his father were flown to hospital.
The regional government said the boy was in intensive care with serious injuries.
"The father is in hospital with the child," Marina Volkova, the Kamchatka Territory's deputy minister of health, said. "The day before, they flew in from Vladivostok."
