In recent weeks, hospitals in Washington, D.C., Los Angeles, Colorado, Nebraska and New Jersey have reported an increase in cases of MIS-C cases, a rare inflammatory condition found in children. The apparent uptick in MIS-C cases coincides with a decrease in COVID-19 cases nationwide, in the wake of a post-holiday surge. But experts interviewed by ABC News explained that there is often a lag -- sometimes three to four weeks -- between COVID-19 infections and the onset of MIS-C symptoms.