The number of uninsured children in America has grown for the first time in nearly a decade, despite a strong economy in which more people have jobs with access to employer health-care coverage. Roughly 276,000 more children were uninsured in 2017 than the year before, bringing the total to just under 4 million, according to figures in a report released Thursday by Georgetown University’s Center for Children and Families. Some 5 percent of children and teens under the age of 18 had no health-care insurance, up from 4.7 percent a year earlier. “With an improving economy and a very low unemployment rate, the fact that our nation is going backwards on children’s health coverage is very troubling,” said Joan Alker, the center’s executive director. “Without serious efforts to get back on track, the decline in coverage is likely to continue in 2018 and may in fact get worse for America’s children.” Alker attributes the drop to the Trump administration’s attempts to dismantle the Affordable Care Act and shrink Medicaid.