Gum Fung is located where KB Gardens used to be and is now the destination dim sum in New York. When you go, be sure and try to get seated in the main dining hall (which should be possible without too long a wait since it probably seats 300), rather than the "side rooms" upstair. The carts will come more frequently, the selection will be better, and the food will be warmer.
Thought Gum Fung was a good place to bring kids. Not only is it big enough for kids to have fun walking around, but on the Sunday we went they were blowing up balloons for anyone who asked.
Final nice thing. There is a huge municipal parking lot pretty much across the street, so it is possible to drive there.