Not a problem - the same thing happened to me recently. The cut of the second sleeper on the Crescent was planned, but probably not at the time you made your reservations. They are simply moving you to the remaining car, so you will still have the same type of room(s) that you orginally booked. The sleeper cars are identical.Now if you are already holding tickets with the old car and room numbers, you will need to get them reprinted at the check-in counter before boarding. That will minimize or eliminate any confusion with the car attendant when you board.
It is highly unlikey that you could be bumped from your sleeper into coach, the only way I see that happening is if there is a last-minute mechanical problem with the sleeper car and they run a train without a sleeper at all - and that is very, very unlikely. So relax and enjoy your trip!
By the way, as a fellow Amtrak rider I would like to say Thank You for the consideration you are showing by booking a sleeper for your kids. Of course I bet your kids are super well-behaved and wouldn't be a bother at all, but I understand what you mean about noisy kids!
Thanks and have a great time.
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