Pope Francis has lamented that children, as he puts it, are being taught in school that gender can be a choice.
He said: "Today, in schools they are teaching this to children - to children! - that everyone can choose their gender."
Without specifying, he blamed this on textbooks supplied by "persons and institutions who donate money".
Francis weighed in during a closed-door meeting last week with bishops from Poland during his pilgrimage there. The Vatican released a transcript of those private remarks on Tuesday.
The Pope blamed what he called "ideological colonising" backed by "very influential countries", which he did not identify.
One such "colonisation", he said, "I'll say it clearly with its first and last name, is gender".