Finding an alternative source of energy isn't child's play. Or is it? Raj Pandian, a professor in Tulane University's electrical engineering and computer science department, has a patent pending on an invention that places pneumatic cylinders beneath the seats of seesaws. Activated seesaws pump air through the cylinders into tanks where the compressed air is converted into electrical power. Two children playing on a seesaw for a half-hour can generate enough power to operate a laptop computer for 20 to 40 minutes.