I would say that at that age it's a bit irresponsible. I especially don't understand why she didn't hire a babysitter for the night ( I don't think it had to do with financial issues).
Anyhow, If the kids were a little bit older or if it were one child I would let it slide but this seems too much responsibility. especially in New York, in a hotel room, on New Years Eve.
Call me conservative but that's where common sense leads me.