A New York man and his two young children narrowly escaped serious injury on a Northwood lake yesterday. Craig Jankowski was on a 12' aluminum boat with his son and a daughter, ages 5 and 3 when he shifted his weight causing the boat to list heavily and ejecting him. The boat began to circle and struck Jankowski causing propeller abrasions. When the boat stopped he saw his son's life jacket at the stern and lifted the outboard motor bringing his son to the surface; he freed his son from the life jacket and swam to the front of the craft and pulled his daughter from the now sinking boat.  Nearby boaters took Jankowski and his two children to the shore where emergency personnel were waiting.   Investigators say the outboard motor attached to the 12-foot boat was never intended for a craft of this size. This accident remains under investigation.