Just researched this myself and I don't think we'll even use a cab. The hotel we're staying at is so centrally located, we will use subways or buses instead. And, because this is half business, half pleasure, dh is driving down a few days before so if we really need the car, it will be at the hotel. But, I'm not forseeing that at all. Thanks for all the tips and I'll be sure to post pics!
You must live, not simply exist.

we went to nyc a few times with DD, around age 2ish and 2 and a halfish. we used the car seat for longer rides, like to/from the airport. but when just taking a taxi across town we just strapped her in with the seat belt and hoped for the best! it was really weird to adjust to that way, but my friend who lives there reminded me that there aren't any seat belts on the subway or busses, right? everyone does it, but we just did as much walking as possible and kept the cabs to a minimum.

I had this same conundrum when I went on vacation to NYC with my son a couple of years ago. The general concensus of other New Yorker parents that I talked to said that a car seat might be a good idea for longer cab rides, say from the airport to the place you're staying. But when you're around town and will be staying off most freeways, etc., most people said that holding them in your lap was fine. It's just not practical with how tightly crammed New York is and with how much walking is required to always have a car seat to lug around. One thing my husband suggested is that if you are hailing a cab, keep your carseat or your stroller kind of out of sight, because in our experience, drivers didn't really want to hassle with that stuff and so therefore wouldn't pick us up. I was surprised at how well we could get around without the cabs once we reached the city, though, if you feel at all nervous about it still. Good navigation with the subway and bus system will get you most places. Just bring an easily toteable stroller along just in case you have to do a little trekking.

Good luck! I hope your family has a great time!

how old are the kids? i live in brooklyn and while we never take cabs anywhere, i bus and subway or walk, i have a booster seat in my aunts car that i would use if i had to take a cab far a long trip. But you aren't going to carry a big carseat around manhattan, are you?

They might not individually require it, but it is illegal to have a child in any automobile or truck without one. I personally would never want to do it.

edited to add "taxis have a NY State exemption from the child seat laws. But, on the other hand, even the Taxi & Livery Commission says, "Passengers with children are encouraged to bring their own car seats, which the drivers must allow passengers to install. Children under the age of seven are permitted to sit on an adult's lap."