Seventeen days after the children went missing, Petro announced that they had been found alive, but he retracted the statement a day later, saying he had been given false information.
On Friday, he praised "the effective coordination between the military and the Indigenous people" during the search, saying it was an "example of an alliance for the country to follow."
Valencia told AFP that the children had been found by a native of Araracuara who had been participating in the search.
"I need a flight or a helicopter to go and get them urgently," the grandfather said.
Defense Minister Ivan Velasquez paid tribute to the various army units' "unshakeable and tireless" work, as well as to the Indigenous people who took part in the search.