7 day trip to Netherland... should we include Belgium ?

How would you propose to see those four Belgian towns in one day or even two days?

Much of your precious little time will be wasted on getting to and from Belgium and changing accommodation. Those two days in Belgium will effectively be much less.
Maastricht and Giethoorn (mind the spelling!) both involve a lot of travelling time. Why not look for day trips closer to Utrecht?
You can have a nice day out combining Amersfoort, with a lovely historical centre, and Naarden, a wonderfully preserved 17th fortified town.
Have another day for Dordrecht, with its historical river ports, in combination with the windmill complex of Kinderdijk.
How are you planning to travel around: by car or public transport?

Thank you both for you quick response.
a) I came across 1 day trip from Amsterdam to Brussels and on the way back covering a couple attractions in Antwerp.. Departs - 9.30am - Arrives back 9.30 pm
That is what made me start thinking if by giving away 3-4 destinations in Netherlands, I can visit these towns in Belgium.
From both responses it is clear that changing plans and visiting Belgium is not a good idea.
b) I will check suggested places - Amersfoort, Naarden, Dordrecht in combination with the windmill complex of Kinderdijk.
Question about Kinderdijk - If I a planning visit to Zaanse Schans, does it still make sense to visit Kinderdijk ?
c) I am still debating renting a car or using public transport .. For the latter, I found today from NS helpdesk that I can buy a 1 month pass for 27 Euros and add 3 passengers to get 40% discount on each ride. Also ready that driving is not suggested due to traffic jams on motorways and difficulty finding parking.
Thoughts on the mode of transport are welcome.

Zaanse Schans and Kinderdijk are totally different. The Zaanse Schans is an open-air museum with a collection of historical industrial windmills and other remnants of a bygone era. Kinderdijk is a series of windmills for draining the surrounding area still in their original position in an open landscape. (Google for pictures to see the difference.) And for its proximity to Amsterdam the Zaanse Schans can be crowded when some busloads of daytrippers arrives simultaneously. The same is for Volendam and Marken: it can be much too crowded with tourists.
Instead I'd go to Enkhuizen, which is a real gem and not so crowded. It has the lovely open-air Zuiderzee museum. It is only 1hr30 mins from Utrecht on an half-hourly direct train. You can easily combine it with Hoorn, another former port town, 30 mins before Enkhuizen on the same railway line.
I would seriously consider to use public transport. It is a busy part of the world and parking in cities can be a nightmare. You can rely on this real-time public transport planner 9292 for all your connections.

Additional question about "museum week". We were planning to visit a few museums.. and got a suggestion to buy museum card.

http://www.dutchmuseums.com/museumcard.php

But on this site it is also written that during Museum week (Apr 9 - Apr 15) - "Museumcard is not valid during Museum Week!"

We are not able to find an easy way to confirm which museums are in / out and whether coming there and buying a museumcard will be useful or not.

Museums we would like to visit
- Nemo Science Center
- Van Gogh Museum
- Railway museum, Utrecht (Eg: For a family $70 is 1 day admission, so purchasing a MuseumCard makes sense, unless as written above it is "invalid" in week of Apr 9.)
- Nijnetje Museum, Utrecht
- Sonneborgh utrecht

Any suggestions about this ?

Thank you,
Chirag