[Refugees check their cell phones as a child runs atop of a cement wall at a small refugee camp at Pothia port, on the southeastern Greek island of Kalymnos, Monday, Feb. 1, 2016. European countries have been strained by the influx of migrants, leading to disagreements over what to do with the large number of new arrivals and how to share the burden. (AP Photo/Thanassis Stavrakis)]THE HAGUE, Netherlands (AP) — The European Union police agency says authorities dealing with Europe's migrant crisis have lost track of about 10,000 unaccompanied children over the last 18 months amid fears that organized crime gangs are beginning to exploit the vulnerable youngsters.