(NBC) – More than 15,200 children arrived alone in Europe this year after completing dangerous migrant journeys, according to the United Nations.  A total of almost 150,000 people entered Europe seeking new lives during the first nine months of 2017, the U.N. refugee agency, UNHCR, said in a quarterly update titled “Desperate Journeys.” That’s under half the number in 2016, which saw record levels of migration, but it still creates headaches for governments struggling to process arrivals and prevent children from being exposed to exploitation.