The New York-based charity, which raises funds for children in developing countries to receive cleft lip and palate surgery, has so far enabled the operation to be carried out on thousands of kids since it was founded in 1999.
WWAV's involvement will centre on a press, direct mail and door drop campaign to encourage donations to raise cash for the operation, which the charity says takes only 45 minutes and costs $250.
Brian Mullaney, co-founder and president of The Smile Train, said: "We have helped over 164,000 children who were unfortunate enough to be born with a condition that is otherwise not considered to be a medical priority in the countries of their birth."
The Smile Train, which is backed by various American politicians and singers, including George W Bush, Bette Midler and Candice Bergen, supports treatment in 55 countries worldwide, with particular attention paid to China and India.
The condition relates to a congenital deformity caused by a failure in facial development before birth. It can affect between one in 600 and one in 800 babies, with US politician Jesse Jackson, actor Joaquin Phoenix and NBC journalist Tom Brokaw among the more notable celebrities with a cleft.
Marco Scognamiglio, chief executive of WWAV Rapp Collins London, said: "This has certainly put a big smile on our faces.
"It's always incredibly exciting to work on a launch, but the nature of this charity's work and the 100 percent commitment of funds to the cause it supports is a fantastic platform to spring from."
List broking for the campaign will be handled by HLB, with media buying through WWAV Rapp Collins Media.
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