BearX220

I'm going to offer a different opinion.

In the US, a flying trip of < 300 or 400 miles is usually not as quick, simple, or economical as driving or taking ground transport. In late November / early December the chance of weather-related flight disruptions is high. OP has a family of four to transport, so that makes for some costly flying versus driving or training. And he wants to see some of the countryside.

On the other hand it is difficult and expensive to drive into, and park in, New York and Washington DC.

So...

1. Before leaving home, book rental car as a one-way rental, leaving downtown Boston, arriving at Dulles Airport outside Washington four or five days later. (This will make sense when you read below.)

2. Fly into Boston as scheduled. Enjoy the city, but do not pick up rental car until departure day. (You can collect a rental car in-city at rates normally cheaper than airport pickup.)

3. Collect rental car on the day you depart from Boston and drive west. Take two days to drive to Niagara Falls (about 450 miles), stopping over for the night somewhere in the Adirondack mountains.

4. Keep rental car during your Niagara Falls stay, then drive it to Washington DC (about 400 miles), which can be done in one long day. Return the car at Dulles Airport (IAD) outside the city and take the train or Uber into town; this will save you having to navigate a strange city behind the wheel.

5. Do Washington DC and then take Amtrak to New York. Service is faster than flying or close to it, less delay-prone, much less expensive.

6. Do NYC, then either fly home from there, or take the Amtrak to Boston if that's where your return transatlantic trip must commence for cost reasons. (Do not try flying into Boston and landing a few hours before your transatlantic booking leaves... too much potential for delays, missed flights, general upset.)

If feeling adventurous and weather is good, consider bus travel (Greyhound, Megabus, Peter Pan) for at least one leg between Washington, New York, and Boston. Can be very inexpensive when booked in advance online, and it's fun to drive into the big city when you're a passenger.

With this plan there is no backtracking, plenty of scenery, no burden of a car when you don't want one, and the choice of Amtrak or multi bus lines once you reach Washington.