Hi Chris!
Have fun in "my" city! You've had all kinds of lens advice. As many have said, shooting in NYC is mostly a "wide" affair. I would suggest that if you can find one second hand to look into the Zenitar 16mm fisheye. It's relatively inexpensive, and tho it is a manual lens it's not that hard to use. To be truthful, because the lens was designed for a full frame film camera, the fisheye distortion isn't too bad and can be compensated for with careful framing. That's my two cents as far a lenses goes.
edit: I would get a low light lens if at all possible. Many of the museums here ban flash photography so a good low light lens is a must. Fortunately you can find the M 50mm F1.7 fairly cheaply, it's a good lens to have in NYC.
I don't know how tightly scripted your vacation is and what ages your kids are, but to my mind one of the most underrated "sights" in NYC is a walk across the Brooklyn bridge. It's free and gives you a great view of both mid and downtown Manhattan, NYC harbor, the Statue of Liberty myriad other things besides.
If your family likes books at all, I'd suggest going to Adorama instead of B&H. Adorama is around the corner from the biggest Barnes and Noble I've ever seen. Four large floors full of books, music, magazines etc. It (B&N) is also at the head of Union Square, a nice park where you can sit in the shade or check out the Farmers Market or the many artists selling their work.
Here's a shot of the B&N
If you have any questions regarding NYC don't hesitate to PM me
NaCl(It's my city and I love it)H2O