A prayer read out in churches across France expressed the wish that children "cease to be the objects of the desires and conflicts of adults in
order to fully benefit from the love of a father and mother."
The text was produced by the Bishops of France, who are leading opposition to President Francois Hollande's commitment to legalise gay marriage and make it possible for homosexual couples to adopt children.
Michael Bouvar, one of the leaders of gay rights group SOS Homophobie, attacked the church's move. "The message sent out by the church is a mask for
discrimination and homophobia," he told AFPTV.
The prayer was read first at midnight mass at Notre Dame cathedral in Paris, attended by nearly 5,000 worshippers ahead of the traditional
candle-lit Assumption procession on the Seine river.
It was also read out to some 20,000 pilgrims at Lourdes in southwestern France.
Bernard Housset, the Bishop of La Rochelle who presided over the 139th national pilgrimage to Lourdes, told reporters before the mass that the church
would continue its campaign against the proposed legislation.
"You cannot confuse the marriage of a man and a woman with the union of two homosexuals," he said.
Opinion polls suggest the church's stance is out of sync with the views of most French people, two thirds of whom back gay marriage.
A narrower majority (53 percent) is in favour of same-sex couples having the right to adopt, according to a poll published on Wednesday by digital
magazine La Lettre de l'Opinion.
The vast majority of the French are of Catholic heritage although only around five percent of the population attend church regularly.