AAP, I checked with my spy on the Spy Museum, you won't need a sign interpreter for the exhibits. All the monitors are captioned, so the students will be able to read what others are hearing.
And $20 sounds about right for ESPNZone for each kid. I know I've ate up that much when playing there.
If you're going to eat breakfast at Union Station, let me know. I live close by and could meet you there for an early breakfast.