MEXICO CITY — Sunday was Valentine’s Day, and even though Pope Francis was in Mexico in the middle of a demanding six-day trip, he still got a card to mark the occasion, presented by a four-year-old girl suffering from leukemia named Ximena Sanchez Torres.

Sanchez gave the pope the card as he was visiting the oncology ward of a hospital in Mexico City on Sunday evening.

The front of the card had a heart with her name in it, along with the words “Welcome Pope Francis” in Spanish. On the card’s back, the names of the children who were at the oncology ward to greet the pope were listed.

“This way, he can pray for each one of us,” she said.

Francis received the card with a smile, asking Sanchez, “You made this? Gracias!”

During his brief visit to the Federico Gomez pediatric hospital, the pope greeted the 38 children on hand with a smile, posing for pictures, playfully mussing the hair of the older ones, and stopping for a chat for those who seemed willing to talk.

“I love you, pope!” one of the patients shouted, to which Francis smiling answered “Then pray for me!”

“On one hand, entering here and seeing your eyes, your smiles, your faces, has filled me with a desire to give thanks,” the pontiff said in a short speech.

“Thank you for the kind way that you welcomed me, thank you for recognizing the tenderness with which you are cared for and accompanied,” he said.

The pope thanked the hospital personnel for taking care of the young patients, “not only doctors, but also those who provide ‘kindness therapy,’ thus making the time spent here more enjoyable.”

Francis briefly played doctor himself, giving five-year-old Rodrigo Lopez Miranda some medicine from a dropper before putting that “kindness therapy” into practice by wrapping him in a grandfatherly hug.

Trying to give hope to the children, Francis told them the story of Juan Diego, the young Indian boy to whom Our Lady of Guadalupe is traditionally believed to have appeared in 1531.

“When his uncle was sick, he was quite worried and distressed,” the pope said. “Then, the Virgin of Guadalupe appeared to him and said, ‘Let not your heart be disturbed or upset by anything. Am I not here with you, I who am your mother?’”

Although most of the exchanges between Francis and the sick youth were in hushed tones and impossible to hear, before he arrived one of the patients, Yessina Cano Valencia, told reporters she was going to ask the pontiff “for a new heart,” since the six-year-old needs a transplant.

Humberto Mendoza Roberto, also six, had a picture of the pope and asked him for an autograph, while Maria Guadalupe Esquivel handed him a picture of Our Lady of Guadalupe.

The hospital is the same one St. John Paul II visited in 1979.

During his foreign trips, Francis often stops at children’s hospitals even when it’s not in the program, as he did in the Central African Republic last November.

On such occasions in the past, Francis often has been asked why children suffer, and he’s readily confessed that he doesn’t have an answer.

For instance, when he was in the Philippines in March 2015, a former homeless girl told Francis that there are many kids who become victims and many terrible things happened to them like drugs or prostitution.

“Why is God allowing such things to happen, even if it is not the fault of the children?” 12-year-old Glyzelle Palomar asked Francis.

“She is the only one who has put a question for which there is no answer, and she wasn’t even able to express it in words, but in tears,” the pope said.