Up to 20,000 people, including several pro-Kremlin lawmakers, are scheduled to take part in the "March in Defense of Children," where they will demand that the government improve conditions at the nation's orphanages and make it easier for Russians to adopt.
They will also gather signatures for a petition asking President Vladimir Putin to secure the return of Kristopher Shatto, a two-year-old Russian boy adopted by U.S. parents last year.
Shatto's older brother Max, 3, died in January, sparking an ugly war-of-words between Russia and the United States about the safety of thousands of Russian children adopted by U.S. parents in recent years. Russia banned U.S. adoptions as of Jan. 1.
The march is being organized by a movement called "Russian Mothers" and enjoys the support of outspoken children's ombudsman Pavel Astakhov, as well as wrestler-turned-State Duma Deputy Alexander Karelin, who recorded a video endorsement for the march's website.
Participants will begin the march at 2 p.m. on Gogolevsky Bulvar, near the Kropotkinskaya metro station, and walk along the Boulevard Ring until they reach Pushkin Square, where a rally is scheduled for 3 p.m. to 5:30 p.m.
Meanwhile, up to 4,400 opposition activists, including veterans of the street protest movement, are scheduled to take part in a demonstration dubbed the "March for Muscovites' Rights."
Unlike earlier large opposition protests, which were mostly directed at President Vladimir Putin and the ruling United Russia party, Saturday's event will focus on local issues facing Muscovites.
In particular, marchers will demand that City Hall increase the public's role in regulating construction projects and selecting officials, including the mayor. They will also press Mayor Sergei Sobyanin to improve public transportation, raise pensions, and boost salaries for state employees.
The opposition march will begin at 2 p.m. on Strasnoi Bulvar, near the Pushkinskaya metro station, and continue along the Boulevard Ring to Prospekt Akademika Sakharova, where a rally is planned for 3:30 p.m. to 6 p.m.
Participants are expected to include activists from the Western-leaning Yabloko party, Solidarity, the For Human Rights movement, and other stalwart opposition groups. Opposition leader Sergei Udalstov, currently under house arrest, are among the event's organizers.
Nearly 14,000 have signed up on social networking sites to attend the demonstration.
About 4,000 law enforcement officials and volunteers will be mobilized for the demonstrations, and automobile traffic will be restricted on the Boulevard Ring for the duration, Interfax reported.