This site is great, are you travelling Inderpendent? or with Key/Eurocamp?
We went with Keycamp in a tent in May 2005, i then sent my brother and family in Sep.
Train to Amsterdam goes from Leiden, depends on how good a cyclist you are (look on multimap) otherwise drive. We however drove to a Park and Ride just outside Amsterdam you can park for 5 euros and then get a 2 free tickets into the city via train,bus or tram (these all depart from within 100mtrs of car park) if you do decide to park and cycle make sure you see the attendant at the car park as the reduced (5euro) parking fee is only valid if you get the ticket from him stamped at one of the train stations in the city. We found this was a much easier and cheaper way to visit the city.
Now, the campsite, the only bad thing is that it isn't in France!!. it is the most wonderful place for kids who are active. it also a load of fun for 30yr old kids too!!. Make sure you go on the open top 'Splash' ride.
The swimming complex (Tikibad) was free to use for 2 hrs between 10am and 2pm. it can get very busy at times so it is best to have a peep through the windows to see before going in the brillant thing was we were only 3mins walk from the tent so it so convenient to do this.
The site is massive and my advise would be to make sure that you get allocated the best pitch on arrival. We were next to the Bar/Supermarket and supprising we had no trouble with noise.
Washblock were very clean and well maintained as was the general site.
Outside of the camp there is loads of cycling to be done, lovely resturants to find and general exploting, it certainly is worth while hiring a bike (available on site) to get around if you don't have your own. Wassener is fine for shopping, with a 2 decent supermarkets and a great selection of bakers,butchers, delis. There is 2/3 seperate parts to the town for shopping so make sure you look down all the street!! there was a big piece of building going on when we were there and i can't remember if my brother said it was finished (this may be more shops, can't remember).
Could go on more. if you have any specfic questions then i would be happy to answer as i said earlier this is a wonderful site and you will not be dissapointed. i hope!!