Alfie Evans, 23 months old, has been in a coma for over a year and needs a ventilator to keep him breathing due to a rare degenerative neurological condition.
His parents are fighting a court ruling that would allow doctors at Alder Hey Children's Hospital in Liverpool, northwest England, to turn off the ventilator.
The parents, Tom Evans and Kate James, attended the Pope's weekly general audience at the Vatican on Wednesday.
Pope Francis spoke during the audience of Alfie's case and that of Vincent Lambert, whose parents are also fighting a court ruling to withdraw his life-support in France.
"I would like to draw attention to Vincent Lambert and little Alfie Evans again," he said.
"I want to reiterate and strongly confirm that the only master of life, from the beginning to its natural end, is God, and our duty is to do everything to protect life."
On Sunday Francis had called for "the dignity of every patient to always be respected" and for them to "be treated appropriately for their condition".
The UK High Court ruled in February that doctors could stop treating Alfie.
The decision was upheld in the country's Court of Appeal and Supreme Court.
Alfie's parents wanted the European Court of Human Rights to examine the case, but ECHR judges dismissed the case.
The little boy has been hospitalised since December 2016, suffering from chronic seizures.
More than 125,000 people have joined a Facebook group supporting the campaign to keep him on life-support.