This suggestion is too late for the OP, but for any other parent looking for ways to entertain a 4-year-old, if you need some free entertainment, hit Heckscher Playground in Central Park. It's right up any 4-year-old's alley and will kill at least an hour of time. It's also a good stopping point before or after a visit to the Museum of Natural History and its great dinosaur exhibit. That, too, is usually popular with the 4-year-old set.