They cross six thousand miles of desert and sea to reach Europe, children travelling alone, on the world's most dangerous migration route. Some of them are as young as seven. Panorama's Paul Kenyon travels to the place they're fleeing, the border area between Sudan and Eritrea, where four thousand migrants cross each month, trying to escape Africa's most secretive rogue state. With exclusive access to desert refugee camps, and to the Sudanese border patrols, Kenyon discovers that more lone children than ever before are attempting the route. Some are recruited by the people-trafficking gangs because they are too young to be prosecuted by the European authorities. Panorama speaks to one such 15-year-old who piloted a boat across the Mediterranean with nearly 200 migrants on board.