Pope Francis' book for children has been published today around the world.

Dear Pope Francis is based on letters received from 259 children in 26 countries, written in 14 different languages. Each child had illustrated his or her letter with a drawing.

The project saw Pope Francis sitting with Father Antonio Spadaro on an August afternoon in Rome and going through a selection of the letters one by one. He personally answered 30 of the questions, though he said he wished he could have answered them all.

One of them, from 10-year-old Mohammed, a pupil at a Jesuit-run school for Syrian refugees, begins: "Will the world be again as it was in the past?"

In part, Francis answers: "There are those who manufacture weapons so that people fight each other and wage war. There are people who have hate in their hearts. There are people who are interested only in money and would sell everything for it. They would even sell other people."

More to Mohammed's point, Francis answered: "No, when the time comes, the world will not be as it was. It will be far better than it was in the past."

Another child, seven-year-old William from the US, asked, "If you could do one miracle, what would it be?"

"Dear William," the pope said, "I would heal children. I've never been able to understand why children suffer. It's a mystery to me. I don't have an explanation."

Another, eight-year-old Natasha from Kenya, asked how Jesus walked on water. "You have to imagine Jesus walking naturally, normally. He did not fly over the water or turn somersaults while swimming," he wrote. "He walked as you walk!" Francis added: "Jesus is God, and so he can do anything!"

An eight-year-old Australian boy, Luca, had a poignant question. "Dear Pope Francis, My mum is in Heaven. Will she grow angel wings?"

Francis answered that no, she won't grow wings, but "she is the mother you know but more beautiful than ever... smiling and full of love for you".

The pope's responses were not edited or condensed for the book, published by Loyola Press in the US and by Rizzoli in Italy.

Francis met some of the children who contributed to the book on Friday at the Vatican, who asked him questions ranging from "How old are you?" to "Is it easy being the pope?"