OP,
I've done the Macy's Day Parade for years. You should get there at 6 AM to get a spot on the parade route (not all of you, at least one of you). They close off some streets if there are crowds. We missed it one year, it was warm and tons of people came ... they blocked off the parade route and we couldn't meet our friends who'd gone earlier to save us a spot.
The trains are crazy crowded, it's the busiest weekend of the year to travel. One year, I was on a MARC train from NYC to DC. No room for bags! The seat was hard, my back hurt for days.
The hotels are expensive, the train, too.
That said, it's a blast.
How old are your children?