As we say in today's paper, most school systems decided not to have their students come back for one day before winter break.   Baltimore and Harford were the exceptions. School systems argue that the snow on side streets and sidewalks would mean students were walking in the street.  Not all city streets, in particular, have been plowed. We interviewed some parents who would have preferred not to have their sweet creatures underfoot in the windup to the big holiday. How do all those kids feel though?