quasimodo tours from bruges to the western front/ypres is excellent.

I agree that you should allow at least 4 days in Amsterdam...and I'd buy a FODOR'S Guide to Holland/Belgium and ask each kid to pick out something they want to see/do in each place so that they do some of the research. Send them online!

Absolutely add GHENT to your itinerary. It's charming and has ancient guild halls along a canal very close to center of town. There is a Gravenstein Castle near there that is interesting to visit--they have a display of instruments of torture that your teens should find compelling. There is also a Gravenstein Hotel that I've stayed in that was quite nice--and there is a brand new Marriott, assembled from old buildings, right on the canal across from the old guild halls.

One of the most famous of all works of art--The Adoration of the Lamb by Jan Van Eyck--is in a cathedral in the center of Ghent. They have English audio guides that tell the fascinating story of this large painting--stolen by Napoleon, stolen by the Germans, panels stolen by thieves. It's in amazing condition, considering that it was painted in 1432 and what it's endured.

Note: Ghent, Brugges and Antwerp are just a 30-minute train ride from Brussels so all are quite close.

This is a very small sidenote but something I'm guessing your kids would be fascinated with...

By chance I saw absolutely amazing street performers (firedancer duo) on Leidseplein square one evening. Very edgy very exciting show. I just happened to be out walking around. This is nothing you'd find in a guidebook.

Don't be afraid to ask your hotel front desk people for ideas about things like this, or pick up local entertainment guides after you arrive.

I took a quick trip to Amsterdam...not impressed. Bruges was nice, Brussels was OK, but Ghent was nicer than both of them without the enormous crowds. If you've got Rick Steves, you have some walking tours. Absolutely add Ghent to your line up...it is a less crowded version of Bruges. I enjoyed our trip but Amsterdam on a national holiday was just nothing too interesting. I'm sure it is different on a normal day.

Search for my thread asking some of the same questions...some good info.