Pope Francis, 86, has previously said he wants to visit Kiev as well as Moscow on a peace mission.
Ukrainian Prime Minister Denis Shmyhal met the Pope at the Vatican on Thursday and said they had discussed a “peace formula” proposed by Ukrainian President Volodymyr Zelensky.
Shimhal also sought help in returning the children to their homeland. Kiev estimates that some 19,500 children have been taken to Russia or Russian-occupied Crimea since Moscow’s invasion in February last year, which it condemns as illegal deportations.
“The Most High is prepared to do this (help bring the children back) because it is the right thing,” Francis said on the plane. “All human gestures help but gestures of cruelty do not help. We have to do all that is humanly possible.”
Francis, who appeared to be in relatively good condition during the visit, also spoke about his health after being hospitalized in late March with what the Vatican said at the time was bronchitis.