VATICAN CITY (CNS) -- When a group of children sang a belated "Happy Birthday" to Pope Francis and gave him a big cake, he needed to think twice before not eating some of it before lunch.

"The cake looks good," the pope told children served by the St. Martha pediatric clinic at the Vatican. "Can we eat it? Yes? All of us? Or should we wait? Let's wait, it's more prudent."

And, in fact, after their audience with the pope Dec. 22, the children's celebration continued with lunch and with gifts. And, presumably, a piece of cake.

Meanwhile, Pope Francis went to the Apostolic Palace to lead the recitation of the Angelus prayer with thousands of people gathered in St. Peter's Square.

The pope's morning meeting with the children was billed as a pre-Christmas greeting, but the little ones also used it as an opportunity to mark the pope's 83rd birthday, which was Dec. 17.

St. Martha's Dispensary opened at the Vatican in 1921 when a New York woman, Dula Draeck, asked Pope Benedict XV for permission to begin distributing milk to poor children in Rome. Draeck's family owned Drycko, which produced powered milk. The dispensary grew and now includes a medical clinic serving children from low-income and migrant families.

Later, before reciting the Angelus prayer, Pope Francis offered a short reflection on the day's Gospel reading about how St. Joseph considered quietly calling off his marriage to Mary since she was already pregnant, but an angel appeared to him in a dream and told him not to be afraid.

"At this point," the pope said, "Joseph entrusts himself completely to God, obeys the word of the angel" and takes Mary as his wife.

"This unshakable faith in God helped him accept a situation that was humanly difficult," the pope said. "Joseph understands, in faith, that the baby generated Mary's womb is not his son, but the son of God and he, Joseph, will be his guardian, fully assuming earthly fatherhood."

"The example of this meek and wise man calls us to raise our gaze and press ahead," the pope said. "The surprising logic of God" isn't about making calculations of what people will accept, but of opening their hearts "to new horizons, to Christ and his word."

Pope Francis concluded his address with a word to families, "your families, who in these days of festivity are gathering: Those who live far from their parents and return home; brothers and sisters who try to get together. May holy Christmas be for all an occasion of fraternity, growth in faith and gestures of solidarity with those in need."