The ad, which shows a prematurely aged child sitting on a bed with a man's body in the background, received the accolade in the category sponsored by this magazine at the Campaign Press Advertising Awards.
Robin Wight, chair of the judging panel, said the graphic portrayal of stolen youth had generated impact in a sector where shock tactics had become commonplace.
The ads, which were designed by agency Bartle Bogle Hegarty, were launched in September in newspapers and developed into a poster and TV campaign.
Diana Green, head of advertising and communication at Barnardo's, said: "We've been successful in getting rid of our old orphanage image but the public want something to replace it. So our focus now is on showing what Barnardo's does, such as tackling child prostitution."