Mariah Carey, Britney Spears, 'N Sync, Elton John, and U.S. women's soccer star Mia Hamm are just a few of the celebrities taking part in Nickelodeon's Sixth Annual Help-a-Thon.

The annual event promotes kid volunteerism and benefits Habitat for Humanity, March of Dimes, and more than 20 other charitable organizations. This year's event, dubbed the Big Holiday Help-a-Thon, will be bi-coastal, with a Big Help Holiday Jam dance party taking place in both L.A. and N.Y.C.

The Nov. 22 Los Angeles event will be hosted by Nickelodeon star Kenan Thompson and will feature performances by Spears and 'N Sync. The L.A. Big Help Holiday Jam will also include teen pop acts A'Teens, My Town, and Aaron Carter.

Nickelodeon veteran Mike O'Malley will host the Big Help Holiday Jam on Dec. 11 in New York. During the dance party, kids will be asked to call in to pledge volunteer hours in their communities and nominate their towns for a visit by Nickelodeon's Big Helpmobile. The Nickelodeon special Big Holiday Help-a-Thon will include taped footage from the Nov. 22 event and is scheduled to air on Dec. 11 from 8-10 p.m. ET/PT.

Big Help spokesperson Carey, along with John and Hamm, will join the campaign through the Team Big Help All-Stars, a series of behind-the-scenes looks at how celebrities got involved in volunteer activities and how their personal causes have made an impact. Additionally, the network will continue to focus the program on local volunteer efforts by making hundreds of visits around the country, including 10 Team Big Help Tour stops to refurbish community parks.