NEWTON — Like most mothers, Emer O’Shea did not expect that her daughter would learn about homosexual lifestyles in her third-grade classroom.

But in her Newton public school last year, she did. What happened is a lesson on the need for more parents to find a voice, according to those fighting against the erosion of parental rights.

More and more Christian parents are grappling with this problem nationwide, and especially in Massachusetts, where lawmakers in July quadrupled the 2007 budget to nearly $2 million for school programs aimed at “outreach to” and “support and safety of gay and lesbian students.” Lawmakers also created a permanent Commission for Gay and Lesbian Youth that will oversee how the money is spent and is not subject to the control of any other department.

Half the Bay State population identifies itself as Catholic. However, three publicized cases here sound an alarm that parental rights — their rights to explain about human sexuality privately and within a moral context — can be superceded by educators promoting the homosexual lifestyle.

These cases represent the tip of the iceberg, said a spokesman for MassResistance, a Waltham-based parents rights group.

The O’Sheas’ story came to light in a Nov. 8 Newton TAB article by Tom Mountain, a father with children in the Newton public schools and a columnist for the weekly paper for four years.

“Cases like this could happen anywhere in the state. Newton has a strong gay lobby, but what happens here today will occur five years down the line elsewhere,” he said in an interview. Mountain predicted that as more states protect marriage by constitutional amendment (there are now 27), homosexual educators will naturally move to Massachusetts, the only state to allow same-sex marriage.

“For every Emer O’Shea who sticks her neck out like this, there’s 100 more who don’t — but want to. She was the first parent in two years who was willing to go on the record,” he said.

What motivated O’Shea were the events that ensued after a Franklin Elementary School social worker, explained about transvestites and transgenders to her daughter’s class. The girl was confused and feared that her baby sister would turn into a boy, according to the article.

A state law mandates that parents must have the chance to opt their children out when discussions of a sexual nature will occur in the classroom. But school officials said that parental consent did not apply in this case, as it was an unplanned “teachable moment.”

Mountain didn’t buy that explanation, as the social worker was a former board member of GLSEN, the Gay Lesbian and Straight Education Network, who specialized in “integrating GLBT (Gay Lesbian Bisexual Transgender) issues” in the elementary years.

For 10 months, O’Shea tried unsuccessfully to get assurances that similar subjects inappropriate for children would not be brought up again. Finally, she raised the issue publicly at a curriculum night for parents.

“That night nobody backed me up, but the next day at the school people thanked me for bringing it up. I got calls and e-mails with the same message,” she said in a Nov. 21 e-mail.

She credits a friend at her church, St. Bernard Parish, for giving her the confidence to go ahead. “After the column came out I got a huge amount of calls again, thanking me for bringing attention to what had happened,” she said.

Meanwhile, however, she removed her daughter from public school and enrolled her in a parochial one.

“I think people don’t talk out openly as they don’t have another schooling option and they are afraid their child would suffer consequences if they speak up.” When they do try and meet resistance, O’Shea said, they “become resigned to the fact that they don’t have a choice or a voice.”

Speaking out is difficult. Both she and the journalist were publicly rebuked in a Nov. 15 Tab guest column submitted by Rev. Richard Malmberg, pastor at The Second Church in Newton, United Church of Christ, and chairman of the Newton Interfaith Clergy Association.

“Gender configuration of the parents is irrelevant to what makes a family,” he wrote. Rev. Malmberg charged O’Shea with “an attempt to derail a school meeting to press her own agenda” and said Mountain had “reached a new low in mean-spirited narrow-mindedness.”

Mountain said that it’s pressure such as Rev. Malmberg’s letter generates that intimidates more parents from defending their values in the public sphere. “Everyone expects everyone else to do it, and there is no one else to do it. It’s just going to take parents saying they’re not going to take it anymore,” he said.

Four other parents who have publicly spoken up against their young children being presented with material by homosexual activists were David and Tonia Parker and Rob and Robin Wirthlin. Both Lexington couples filed a federal civil rights lawsuit in United States District Court in Boston in August against the town and school officials.

Just how high the stakes are in the battle for parental rights became clear in October, when their suit was opposed by the Massachusetts Teachers Union, the ACLU and national homosexual advocacy groups.

Following the TAB article, Parker issued a statement through the MassResistance Web site: “We have arrived at a time in history where school administrators are preaching the gospel of human secularism to their captive audience in the public classroom,” he said in part. “I don’t know what disgusts me more: those who do this to children in our public schools or the parents who watch silently and do nothing.”