I have just booked to go again next year and can't wait.
A good place to visit off site is Maurodam (sp??) a huge model city....sounds naff but trust me it is great, with increadably detailed models of things like Shipol Aitport, complete with a/c that taxi out! Quite amazing and well worth a visit.
If the weather is iffy there is a sealife centre in Shrevingen. The bulb fields are quite nice, and the guardens there have a very good play area, lots of places to run around. Amsterdam is about 45 mins to an hour away, but we haven't don't that with the kids yet, might do it this year.
TBH there is loads to do on site, and you also have the option to hire bikes/go carts and ride around the miles and miles of totaly flat cycle paths.
We have a great time. If anything my two enjoy it more than Disney.
Don't rely on the shop on site for most of your food, as although it is OK for basics, it isn't that good. We stock up in city europe in Calais. Food on site resturant isn't that good. We don't find Dutch food that inspiring.