Nearly 80 percent of girls in Niger are married by the age of 18. It is the highest rate of child marriage in the world and now the African Union has launched a major campaign to end the practice across the continent. Our special correspondent Fergal Keane reports from the remote desert north of Agadez girls are often sold by families desperate for the money they can get. Subscribe www.youtube.com/bbcnews Check out our website: www.bbc.com/news Facebook: www.facebook.com/bbcworldnews Twitter: www.twitter.com/bbcworld Instagram: instagram.com/bbcnews