New York City doesn’t shut down when the Christmas decorations come down. January and February can be wonderful months to visit if you don’t mind bundling up. You can spend a morning in a museum, see a Broadway matinee, go skating, and warm up over a good meal without building your entire trip around holiday crowds. I went into the city often during my kids’ February school break to spend time with family. Those visits taught me to plan winter days differently: choose one substantial indoor activity, add a little time outside if the weather cooperates, and leave room...