WASHINGTON — (CNN) Pope Francis has denounced the teaching of gender identity to young children in schools, calling it terrible.

“Today, in schools they are teaching this to children — to children! — that everyone can choose their gender,” he said in a closed-door meeting to Polish priests and bishops in Krakow last Wednesday.

The Pope blamed textbooks supplied by “persons and institutions who donate money,” for spreading gender theory, calling it “ideological colonization, supported by very influential countries. This is terrible,” he said.

Pope Francis said he had spoken with Pope Benedict about it, who told him, “This is the age of sin against God the Creator!”

Pope Francis has previously spoken against gender theory saying, “Getting rid of the problem is not the solution.”

In April of last year at a general audience in Rome, the Pope said, “I wonder if so-called gender theory may not also be an expression of frustration and resignation that aims to erase sexual differentiation because it no longer knows how to come to terms with it.”

New Ways Ministry, an LGBT advocacy group, criticized the Pope’s remarks.

“The pontiff’s remarks are further evidence that church officials need desperately to educate themselves about the lives and experiences of LGBT people,” said Francis DeBernardo, executive director of New Ways Ministry.

“Nobody chooses a gender identity. They discover it.”

DeBernardo called on the Vatican to establish a commission to “update their understanding of gender identity and sexual orientation.”