There truly is loads to do! Lived there for a couple of years (with kids) and would recommend science museum (although not specifically Dutch, of course!), Ship Museum, both very close to Central Station, Zaanse Schans is very touristy but great if you want to get the windmill, cheese, clogs thing out of the way in one go. The Zoo (Artis) has some very old-fashioned housings, I remember the monkeys being stuck in Victorian cages but I think they were overhauling because parts of it were v-modern and they had a great outdoor play area beside the cafe. The canal trip is good because it is about an hour so you get just long enough to rest your feet but not so long that the kids get bored. Anne Frank house probably best from about 6-7 upwards so they can actually understand and appreciate it but also v-popular so get there early. The Rijksmuseum and Van Gogh museum are very close to each other and also to the entrance to Vondelpark so if all that ure becomes too much they can go in there and run off steam.