The creative was unveiled in London yesterday by Lord Puttnam, UNICEF UK president, with Lord Attenborough, UNICEF's goodwill ambassador.
Paul Meyer, global president of Clear Channel Outdoor, said he knew "no better way to use the world's only true global outdoor network".
The campaign will run on posters, street furniture and bus-sides in 50 countries worldwide, starting in November.
The creative is the result of a worldwide competition between 300 advertising agencies, which saw Bester Burke, from Cape Town, South Africa emerge as the winning agency.
At events in Johannesburg and NY, synchronised with the London launch, celebrities and representatives of Clear Channel and Unicef met to unveil the shocking image of a child standing by the graves of her parents.
In New York, Sir Roger Moore and Whoopi Goldberg, both Unicef goodwill ambassadors, turned up to kickstart the campaign with Chaka Chaka in attendance in South Africa.
Unicef executive director Ann M. Veneman said: "Children are disproportionately impacted by the HIV/AIDS pandemic.
"The Clear Channel Outdoor partnership will help make the public aware that children are the missing face of Aids."
Phoenix-based Clear Channel Outdoor is a global leader in outdoor advertising with 800,000 displays in more than 50 countries across six continents.