Thought I'd throw in my $ .02 based on my experience....I had my first trip ever to NY City in Feb. '05. It was absolutely wonderful....EVERYTHING....I was like a kid in a candy store. I stayed at the Manhattan Club, was surprised by my hubby showing up unexpectedly - it was only supposed to be "the girls" for 4 days and they were coming on the tail end - anyway....my sisters and I LOVED it.
So...we thought bringing the kids to NY would be a great idea and therfore planned our trip for Aug. 05 with some of our children. I only brought my 2 oldest (9,7 boys) my sister brought her middle (8 girl), and my other sister brought her oldest (8 boy). We were certain they would have a grand time because they were "old enough" to appreciate it all.....
Let me preface before I go on......my own family frequently takes trips into the "big city" of Chicago and the boys love it when we do our long weekends down there, so maybe it was just a timing thing with NY, but my experience on our big trip to NY at the tail end of last summer was.......
The 8 yo girl slept during a Broadway matinee (Beauty & the Beast - which I loved by the way). My 7 yo son slept more than half of the double decker city bus tour of Manhattan. The lines were sooooooo long at the Empire State Bldg. that after 1+ hours, we ended up just doing the Skyscraper ride thingy and I still have the "unused portion" of the ticket to the observatory. The loonngg lines for the Statue of Liberty tour (which we booked way in advance and had one of the 1st tours of the day) made the children more antsy and unappreciative than I would have expected. Riding the subway in February smells alot better than riding it in August.

......So, you get my drift....
Now, I do acknowledge all people are different. I can guarantee you there are 6 year old children out there more mature than my 2 oldest boys so I take everyone's experience with a grain of salt. Each person/child is different and only you know your own kids. I thought my kids would enjoy it because they do enjoy our weekends in Chicago with Mom, Dad & the 4 boys......maybe it was the dynamics of the "2 aunts & cousins" vs. "dad & 2 other brothers".
I'm not sorry we did it (although the hubby has a field day saying "I told you so"), but I'll think twice the next time I have such a great time somewhere that I become "certain that the kids will enjoy it as much as I did".
MissTins