ROME – Pope Francis celebrated his 81st birthday with a pizza party for sick children Sunday, reflecting on the joy of children and the importance that they are raised with the faith.

“The joy of children is a treasure,” he said Dec. 17. “And we ought to do everything so that they continue to be joyous.”

“A joyous spirit is like good land that grows life well, with good fruit,” he said in his Vatican meeting with the children being treated by the Pediatric Dispensary of Santa Marta.

Francis encouraged the children to speak with their grandparents. Grandparents “have memory, have roots, and it will be the grandparents that give roots to the children,” he said.

He asked that the children may not be “uprooted children, without the memory of a people, without the memory of the faith, without the memory of so many beautiful things that have made up history, without the memory of values.”

“And who will help children to do this? The grandparents,” said the pope, adding that the elderly “love us very much.”

He exhorted parents to “teach them to talk with God.”

“May they learn to pray, to say what they feel in their heart,” Francis said. “It is joy, to talk with the grandparents, with the elderly, and to talk with God.”

He then encouraged the children to eat the pizza, saying it will make them grow.

Before eating, he prayed the Hail Mary with the children.