The Pope has condemned countries that allow children to choose their own gender, describing it as "ideological colonisation".
He said it was going against the will of God who had created "man and woman".
In a meeting with Polish bishops during World Youth Day celebrations last week in St Stanislaus and St Wenceslaus cathedral in Kraków, Pope Francis laid into "gender" politics.
"In Europe, in America, in Latin America, in Africa, in some Asian countries, there is ideological colonisation," the Pope said. He was particularly concerned about children.
"At school you are taught this: that each one can choose their sex." He said money given by "institutions" was at the root of it. "It is ideological colonisation, also supported by influential countries. And this is terrible."
He had discussed the issue with his predecessor Pope Benedict XVI, who he said was well and thinking clearly, who told him: "Your Holiness, this is the age of sin against God the Creator."
Pope Francis said: "God created man and woman; God created the world so, so, so ... and we are doing the opposite."
He was responding to a question on refugees from Auxiliary Bishop of Koszalin-Kolobrzeg Christopher Zadarko, who asked: "How can we help them, because they are so numerous? And what can we do to overcome the fear of their invasion or assault, which paralyses the entire society?"
Addrdessing the question of what gender politics had to do with refugees, Pope Francis said: "It is context."
He added: "The problem is the world. The exploitation of creation, and the exploitation of persons. We are living a moment of annihilation of man as God's image."
His solution was prayer. "We can have an open heart and consider the introduction of an hour of prayer in parishes, one hour per week, adoration and prayer for immigrants. Prayer moves mountains."
Archbishop of Łódź Marek Jędraszewski also asked him about how bishops should respond to Christians becoming increasingly a minority within a "liberal-atheist contemporary culture".
The Archbishop said Poland was an example of "a huge fight between faith in God on the one hand, and on the other a thought and ways of life as if God did not exist."
Pope Francis said: "It's true, the de-Christianisation, secularization of the modern world is strong. It's very strong."
Some "manifestations of religiosity" could also be a hazard, he said.
"I think that we, in this secularised world, we also have the other danger, the gnostic spiritualisation: This secularisation gives us the opportunity to grow a somewhat gnostic spiritual life."
Pope Francis recalled that gnosticism was the first heresy of the Church, battled by the Apostle John.
Responding to another question from Archbishop of Gdańsk Slawoj Leszek Glódz, Pope Francis also warned against religious illiteracy and shrines that capitalise on people who seek "salvation in superstition".
To another questioner he extolled the virtues of the parish.
"The parish is still valid! The parish must remain: is a facility that we must not throw out the window. The parish is the very house of God's people, one in which he lives.
"The problem is how to impose the parish! There are parishes with parish secretaries who seem 'disciples of Satan', which scare people! Parishes with the doors closed. But there are parishes with the doors open, parishes where, when someone comes to ask, you say: "Yes, yes ... Come in. What's the problem?...". And you listen patiently ... because taking care of God's people is tiring, it's tiring!"
