The London Transport Museum is every vehicle mad boy's nirvana. My oldest son hasn't been totally vehicle crazed in years, but he loved it and has told me many times since that it's his favorite museum yet.
Before entering, we had to queue up with every other mother and set of children in London. Because it was half-term last week for a number of little English kids, many of them were out and about seeing the sites like we were. But the museum is used to children and did a good job of keeping things moving along. They also handed out "passports" to each child that they can get punched at various stops along the way. The children loved this, although the punch machines were so stiff that none of my children could work them without help.
Kids climb on old buses and subway cars, pretend to drive buses and subway cars and even, once in a while, pick up a little history of transportation. The Museum starts you in the 1800s, when chairs carried by a man in front and a man in back were the norm for those who could afford them and every one else walked. Kids can climb in a model omnibus, complete with shaking and jolting movements, test the difference between pulling an omnibus on a cobbled street and over a track and see models of some of the other vehicles of the time, like the two wheeled hansom cab.
Down the stairs, you enter the age of steam and there is a nifty model of workmen tearing up the street and tunneling down to build the subway system of London. You learn about some of the innovations designed to keep the smoke and steam underground to a minimum (using coke instead of coal, using cooling pipes to re-collect the steam and use it as water again, big vents in the street to release the steam into the above ground world) -- or your child races straight on to the old wooden subway cabins. Either way, they are pleased.
Down to the ground level now, you arrive in the twentieth century, where one is greeted by the fact that by 1901, over 4.5 million people lived in London. Okay, the kids were unimpressed. They just raced on to the antique double decker bus where they all wanted to troop up to the top and get a look around.
More buses, more subways, driving things and looking at various other transportation stuff and the end is in sight. It was a few hours of vehicle-mania and thoroughly enjoyed by all the little set.