McALLEN, Texas—Adults using unrelated children to gain quick access to the United States after crossing the border illegally became a problem during the 2019 border surge. This year has all the hallmarks of a repeat, border experts warn. In one 2019 case, a Honduran man bought a 6-month-old baby in Guatemala to pose as a family and get priority release. In another case, a child-for-rent recycling ring was operating between Houston and Mexico. At the time, the Department of Homeland Security set up rapid DNA testing, which revealed a 30 percent rate of fraud in the two test areas of El Paso and Rio Grande Valley, Texas. Homeland Security Investigations, a division of Immigration and Customs Enforcement (ICE), sent 400 agents to the two regions in mid-April 2019 to interview families that Border Patrol suspected were fake. Over eight weeks, HSI agents identified 5,500 fraudulent families—about 15 percent of all …