Might be ever so slightly more efficient to go to Haarlem first from Amsterdam Central, then to Utrecht, then to Duesseldorf. The ICE trains from Amsterdam stop at Utrecht on the way to Duesseldorf.

I personally think Cologne is better for children, but I like Dusseldorf. There's a certain orientation to pub life in Dusseldorf, but children are always welcome at your table in Europe. It's still close to the Dusseldorf airport, depending on departure time. Maybe the river walk is nicer in D'dorf, but you can only spend so much time there. Do the children like museums?

Once you decide, book Anne Frank Huis immediately. It is desperately difficult at any time, and August is vacation month in Europe for the Europeans, too. Eurostar prices go up as demand and the date approach. I have visited Haarlem, but I also think Amsterdam has more for children. Why did you pick Haarlem? Because our host, RIck prefers it to Amsterdam? I don't think Edam is ideal for children, but Hoge Veluwe is. See how large a bicycle the ten year old can use at home. There is a shortage of free children's bikes there, I think. Go to the library and see Rick's Netherlands book, it's invaluable despite his preference for Haarlem.

I have visited Utrecht twice as a daytrip by train from Amsterdam. These cities are pretty close to each other. It's the jump from London to Amsterdam that's annoying. At least you don't have to go back to fly home.

Thank you for the help. I actually met a lovely Dutch college student from Utrecht last summer while on vacation in Barcelona. She gave me a few tips for visiting the Netherlands. We were discussing the mass tourism in Barcelona and she shared how Amsterdam is very much the same. She suggested both Haarlem & Utrecht. I really appreciate my kids getting to meet locals (especially other children) and seeing how life is in other countries. We met one local in our time in Barcelona, which was disappointing in comparison to our time in Madrid. My idea was that from Haarlem, we could visit the beach as well where I would hope to find locals. My kids have a great deal of appreciation for art, history and museums but our favorite memories have been on hikes/bikes and meeting others at cafes, parks, beaches. If we can combine to two..that's a huge bonus!

I have it on my calendar to purchase the Anne Frank tickets exactly 2 months out. =) I just need to purchase the Eurostar tickets ASAP as you have indicated to receive the better pricing.

Thank you for your advice on Edam too. This is exactly the direction I need!

Oh..I might add that in checking into Amsterdam hotels, it seems many are already booked so my only option thus far is about 350 euro per night where we can spend about 40% less on a hotel in Haarlem. That seems like worth the train fare to get back and forth but please direct me to another option if it exists.

I do have the Rick Steves book as well. Thanks, again!

Thanks for your gracious reply. I'm not a huge biker, but I should note that Kinderdijk (besides having local bus service from, I think, Rotterdam) is directly on a national bikeway. We were glad to go inside the renovated windwmill, but I have an idea that a lot of the outdoor viewing may be free of charge. You'll also want to see the adjacent, modern, diesel polder-dewatering pump station.

I have not been to Dordrecht, but I loved Leiden and Utrecht. Don't miss the automated music machine museum, even if you have to take the Dutch tour. They book up. You don't seem to need more excursions, but Delft is not far away, and I also liked Amersfoort, although it has less pure medieval remains. It gives a good feel of local, prosperous, regional Dutch life than Haarlem or Amsterdam. I don't think you have time, but Deventer and the other Hanseatic cities have lovely medieval centers. Two other ideas are the early-morning flower auction in Aalsmeer (fantastic catwalk view of the largest indoor warehouse in the world, all of it plants and flowers), and if the public transit doesn't take too long, the lovely German village of Monschau, from D'dorf. If the children are "urban" at all, they might want to see the Schwebebahn (sp.?) overhead subway in Wuppertal. The train to there was shut down when I was in D'dorf, so I didn't go. Dusseldorf has a monthly Sunday (?) sausage and fish festival on the river walk, check on the August date if you can.

We were underwhelmed by Arnhem. The "bridge" is about the third on that site.

Edit: In case this is of interest:
https://community.ricksteves.com/travel-forum/netherlands/deltawerks-tour

One tip: your youngest one can travel the whole day on the train for EUR 2,50 with a so-called Rainrunner ticket.

Thank you again for all of your suggestions and tips!

We have booked 3 nights in Leiden, 2 nights in Utrecht and 2 nights in Cologne. It is definitely a challenge to find rooms for a family of four but we did it!

Now, back to the day planning and booking train tickets. =)