We recently visited Tokorozawa Aviation Museum, Ebi-kun and daddy loved it, although you wouldn't think so looking at his face in this picture, he had just bashed his leg on that bit of metal!
There are several planes and helicopters in the main hanger, some of which you can climb in and have a good look around.
The museum isn't that big, you can probably do it all in half a day, it is set in a big park so it would be perfect to take a picnic along and have a play outside too. We played football for a while but the wind was bitterly cold!
They have a few flight simulators too but be prepared to wait, we got there early and had to wait 20 minutes to have a go on this one (lasts for 4 minutes) and a similar wait for the helicopter ride. I personally didn't rate the museum as being very good, although, I am only interested in planes if I am getting on one to leave for somewhere exciting! That said, I believe a good museum will capture the imagination of those who are not interested in the subject matter - this place did not. There were a few interactive things for the kids to try, quite a few of them didn't work, the explanations were aimed at adults, not simplified versions with pictures for kids to understand. In Ebi-kun's words, "too much kanji"
The highlight for the boys was the Zero Fighter, this was a special exhibit that you had to pay extra for.
There is a restaurant which has a set buffet, a Imax theatre and of course a gift shop with loads of planes in it - plus toys and kites for the park. There is a discount coupon on the website too.
The boys did enjoy it, myself, I won't be rushing back, if your kids get excited at the train museum they will probably like it here, go on a nice day so at least you can make good use of the park too.