In the capital, the size of the crowd was put at 15,000 to 20,000, France24 reported. Many of the marchers were young.
"We defend our vision of what society should be like. Our first concern is the child's well being and balance," Flora, a student who was there with four friends, told the broadcaster. "If the law passes, it would be a deep injustice to the child, who is not given a choice."
The marches were organized by a coalition, "La Manif Pour Tous," or "The Demonstration For All," and supported by the opposition UMP party, which was ousted in this year's election, Radio France Internationale reported.
The group said it is against homophobia.
Another rally is scheduled Sunday in Paris, RFI reported. It is sponsored by Civitas, a Catholic group whose goal is to "re-Christianize France."