In a giant coat that nearly swallowed her four-foot-something frame, and holding a red stop sign that seemed half her size, LaTanya Long-Sullivan often received hugs from kids and parents, and pretty much any other regular passerby, before shepherding them across the street at the corner of 57th and Kimbark in Hyde Park."Ms. Tanya," as she was known to generations of Ray Elementary School and Chicago Lab School students, was a crossing guard at …