Police are planning to question the adult children of two prominent Democrats as early as today in the wide-ranging probe into who, early on election day, slashed the tires of 20 vans and cars rented by the Republican Party. The investigation has already led to the Tuesday arrest of Opel E. Simmons III, a veteran party activist from Virginia in town to work on John Kerry's presidential campaign. Simmons, 33, was released Thursday afternoon without being charged. Sources told us that police, who are being assisted by the FBI, plan to speak to Michael Pratt, son of former Acting Mayor...