(CNN) -- The archdiocese of Denver, Colorado, is defending its decision not to re-enroll two children in a Catholic school in Boulder next year because their parents are lesbians.

"The Church does not claim that people with a homosexual orientation are 'bad,' or that their children are less loved by God," wrote Archbishop Charles J. Chaput in an article to be published in Thursday's edition of the Denver Catholic Register.

"Quite the opposite. But what the Church does teach is that sexual intimacy by anyone outside marriage is wrong; that marriage is a sacramental covenant; and that marriage can only occur between a man and a woman. These beliefs are central to a Catholic understanding of human nature, family and happiness, and the organization of society. The Church cannot change these teachings because, in the faith of Catholics, they are the teachings of Jesus Christ."

He added people with a different understanding of marriage and family life "have other, excellent options for education and should see in them the better course for their children."

The issue centers on the Sacred Heart of Jesus School, where the children are currently enrolled, the older of whom has been enrolled in kindergarten for next year but will not be allowed to enter first grade and the younger of whom is in preschool but will not be allowed to enter kindergarten.

"The Archdiocese of Denver has acted very unjustly in singling out this child for exclusion," said DignityUSA Executive Director Marianne Duddy-Burke in a written statement Monday, before it became clear that two children were affected. "Until every student's parents are tested on Catholic teaching, this action by Catholic officials cannot be understood as anything other than discrimination on the back of a child. At a tender age, this child has learned that Catholic officials are willing to inflict pain on children and families."

The decision was made public last week.

"These actions by the Denver Archdiocese harm the student by taking the child away from friends, teachers and community," said Jarrett Barrios, president of the Gay & Lesbian Alliance Against Defamation. "It's deeply troubling to see any school remove a child from their educational program simply as the means of rejecting that child's parents."

In a posting of his sermon, the Rev. Bill Breslin, pastor of Sacred Heart of Jesus Church, supported the decision.

"The issue is not about our not accepting 'sinners,' " he said. "It is not about punishing the child for the sins of his or her parents. It is simply that the lesbian couple is saying that their relationship is a good one that should be accepted by everyone; and the Church cannot agree to that."

About 30 opponents of the move, "mostly hetero allies of the gay community," protested Sunday outside the church during Mass, said Dave Ensign, board president of Boulder Pride, a lesbian, gay, bisexual and transgender community center and services organization.

Ensign handed out flyers to the protesters and then joined the parishioners as they listened to the sermon defending the church's move. "I was disappointed, but it was pretty much what I was expecting to hear," he said.

He added that the larger community's reaction has been positive. "When people hear about this, they speak up and I think that says a lot about our community," he said.

The children have not been identified publicly.