Federal authorities are seeking a California woman suspected of kidnapping her 16-month-old biological son and taking him across the Southern Border into Mexico.Brigette Benitez, 31, is wanted by the FBI after she allegedly failed to return her son Miguel Eduardo Zuniga Medina Jr. to his foster family following an unsupervised visit.On Feb. 6, Benitez picked up her son in Walnut, California, for a scheduled, unsupervised visit. But at the end of the visit, Benitez, who does not have legal custody of her son, did not return him to his legal guardian, according to the FBI.The two were last…