Seems silly to answer again when everyone else has answered, but we're all trying to rack up points, right? ;-) Yes, it is accessible, though I would add that the space in the gift shop is also pretty tight for a wheelchair.
Yes, park on the main level. Which is the entrance on 10th street. The main entrance is wheelchair accessible. Once inside there is an elevator. Some of the train exhibits downstairs are not wheelchair accessible due to the exhibit. For example, there are passenger 'cars' from older trains as well as a older steam powered locomotive. Those you can see but a wheelchair woukd be hard to get inside of them.
Just as everyone else has indicated...
Yes, it is wheelchair accessible. There is also an elevator.
can children climb into real trains - and get into the engine?
Yes
Yes it is. There is an elevator to track level.
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