The Netherlands was my kids' favorite country when they were that age. People treat children with great affection. They will love the canals, windmills, etc. We bought wooden shoes for them and one DD loved them so much, we got several sizes. She clackity-clacked around in them for at least three years and was sad to finally out grow them. By that time, we had gotten used to the sound.

So, for a start, buy wooden shoes for them - big enough to wear with very, very thick socks.

The miniature city of Madurodam is wonderful. You will enjoy it too.

In Belgium, you could go to Bruges (and take a canal boat ride or horse drawn carriage) or stop in Ghent. If you spent a couple of nights in Bruges, you could take the train (only a 15 minute ride) to Oostende (Ostend) for a day at the beach. Oostende is a pretty little seaside resort town with a big center square, lots of restaurants and a long beach - perfect for a summer afternoon. Bruge also has fantastic ice-cream.

There are a lot of things to do for children in the Netherlands.
1) De Efteling in Kaatsheuvel (near Tilburg) http://www.efteling.com/
2) Apenheul in Apeldoorn http://www.apenheul.com/
3) Dierenpark in Emmen http://www.dierenparkemmen.nl/nl-nl/
4) Aquazoo in Leeuwarden http://www.frieslandzoo.nl/

Furthermore there are numerous playgrounds (both indoor and outdoor) all over the Netherlands.

Or take the children to the beach when the weather is nice. Both the Netherlands and Belgium have beautiful beaches. Animated beaches (Zandvoort (NL), Scheveningen (NL), Knokke (B) ...) and quiet long stretches of white sand (Groede (NL), Dishoek (NL), Callantsoog (NL), ...).

Where are you staying? Will you have a car or are you relying on public transport?

There are lots of zoos, beaches, playgrounds all over the Netherlands. A lot depends on where you are staying which I would recommend.

Personally I think de Efteling would not be suitable for them. I wouldn't take my grandsons, who are the same age as your children there just yet. Most young children actually find it quite scary, and of course they are too small for many of the rides.

our [slightly older] kids enjoyed amsterdam, and the zoo in particular, as well as the hands on Science museum and the floating chines restaurant nearby. family cycling would also be a possibility - everywhere seems to have special attachments for parents to cycle along with the children in a cart on the back.

@hetismij2
I wasn't actually thinking of De Efteling as amusement park. I think a child of 5 yrs old would enjoy the fairy tale park a lot. The 3 yr old one is simply too young for anything but playing with 'emmertje & schepje' on the beach. But then, that's just my opinion.

MyriamC, I know what you were thinking, but the fairy tale part is very small compared to the rest now, and it is very expensive to visit (imho) for just that small part.

Last time I was there there were young kids who were really frightened in the sprookjesbos. Really really frightened. It was awful to see.

The 3 year old would certainly enjoy a zoo, or some of the playgrounds like Oud Valkeveen or Juliantoren maybe.

Thanks all, you have all given me some wonderful suggestions. We will be staying with friends who live in Delft for the most part and will most likely have access to a car but have no problem using public transport.

Has anyone been to the cheese market in Gouda?

We were thinking of going to Brugges for a couple of days so thanks for the ideas around that.
Any good recommendations on places to stay in Brugges? Here we will not have access to a car.

Carole

Can I recommend Blijdorp zoo in Rotterdam since you are in Delft. I am sure all of you will enjoy it.

Kinderdijk is close by and you can visit some of the windmills.

My 5 year old grandson enjoyed a visit to the Batavia recently: http://www.bataviawerf.nl/startpage.html. You could combine it with a visit to Aviodrome maybe, or the Oostvaardersplassen.
The Biesbosch is not too far from Delft - you could go for a whisper boat trip or rent canoes and explore this unique wetland area.

we really liked Delft, when we stayed there last month.

a nice town, good places to eat [we REALLY liked the Argentinian steak house round the corner from our hotel] and a great bar where they had 6 pages of different beers.

none of that will be any use to your kids, but you might like to know!

Wow, I didn't realize there was a zoo in Rotterdam. It looks amazing! My son would love the Batavia!

Well we started out thinking there wasn't much to do with our kids and now I'm thinking we won't have enough time to fit in so many great activities. Thank you!!

...and yes, we are always interested in finding great places for beer!