How would you spend a week?

If you only have a week, I would focus all the time on the Netherlands, unless there is a specific thing you want to see or do in Brussels. This is for several reasons:

1) It saves time - see places that are closer to Amsterdam.
2) It saves money - local Dutch trains will be cheaper than the train to Brussels.
3) Brussels is often considered a less than stellar place. Of course, opinions vary, but few find it a highlight of Europe (to put it gently). However, my sister-in-law did indeed go to Brussels from Amsterdam, specifically to see some of the artworks there, and was glad she did this. So, if you have a specific reason, that's fine.

Start by looking at Rick Steves Amsterdam & the Netherlands. He has lots of places that make good day trips or overnights from Amsterdam, complete with goof-proof directions, from cities to villages to more rural areas. You can decide which places interest you.

It's hard to give specific recommendations of what to see without knowing your interests.

I'm more of a city person, so I went to Delft, the Hague, Leiden, Utrecht, and Rotterdam. and liked all except for Delft (to me, disappointing and overrated). However, those places won't suit someone looking for nature.

Favorites of mine are mostly outdoors:
A bike ride through the Schoorl dunes (you can rent bikes)

The ferry to Texel and biking around the island (you can rent bikes)

The Zuiderzee museum in Enkhuizen if you like living history museums

Find out when market day is in a village - perhaps Alkmaar

Driving over the Afsluitdijk and wandering through a charming village like Hindelopen

Engineering fan? Take a tour of the Delta Works.

All the stuff in Amsterdam would be based on preference and Ricks recommendations

Enjoy!

Brugge way better than Brussels IMO.

Hard to know what to recommend because we don't know your specifics. But in any case there is more than enough to do in the Netherlands for a week. We based in Haarlem for a week , a short train ride from Amsterdam and also trained all around and had a great time. We spent a lot of time walking around many towns and cities up and down the train line. Trains are frequent and don't require reservations. We just hopped on and off as we pleased. No cash though. Single use OV chip card or a personal OV chip card loaded with credit.(only worth it for multi trips. )

Hopefully you will be able/ comfortable going this summer. For me no way I am going to be traveling , riding trains etc. for quite some time , likely until there is a vaccine or health experts indicate it is advisable. So if you are to postpone you can use the info in the various relies for a later trip. Have fun whatever you decide.

I liked the art museum in Brussels as much or more than the one in Amsterdam. But others are right that the Netherlands has more than enough to occupy yourself for a week. I suggest you look through two or more guidebooks, make a list of the sites that look appealing to you, and post a supposed day-by-day itinerary. You can change your mind multiple times before your trip and possibly at the last minute in the Netherlands. Such an itinerary will give us good idea of what you have time for. One thing I suggest is buy whatever tickets you can in advance - the Anne Frank house and the Van Gogh museum may be the only sight that definitely require advance tickets but for example, after entering the art museum in Amsterdam, I was able to just get my ticket scanned right away rather than waiting in line to buy the ticket, because I bought the ticket before my trip.

Skip Brussels and concentrate on The Netherlands.Stay in Amsterdam and take day trips easily by train to The Hague, Delft, Leiden, Rotterdam and Kinderdijk.

Yep, I agree with the others who recommend focusing on The Netherlands with only 6 or 7 days.
The danger in your situation is that you spread yourselves too thin and are not able to enjoy any of the places because you're too rushed.
In 2018 we did both Belgium and Netherlands but we had 15 full days.

I'm guessing this trip never came to fruition which is sad. When we can go back for the third time I look forward to taking a bike across the water to the North and riding some more. Maybe also to the South along the canal one day.

Richard, there are excellent cycling maps (you might expect that in the Netherlands) available at the VVV (tourist offices) in most large towns. They are done by province so the scale is excellent and very clear to follow. They have a yellow cover and are produced by the Dutch equivalent of the AAA, but a club for cyclists.

Not to miss to my opinion is cycling along the river Vecht north of Utrecht. Especially around Loenen aan de Vecht and Breukelen the river is lined with lovely mansions, you can cycle to “Kasteel de Haar” too. Breukelen is an easy train ride from Amsterdam, or biking all the way from Amsterdam is also possible. Contact the local TI for how to rent a bike and best route options, think the one in Amsterdam can be helpful as well.

Cycling through the countryside to Monnickendam, Edam or Marken is also worth to consider. Volendam is too touristy and not really worth spending much time there, but that's what I think.

The Dutch AAA is ANWB and sells cycling maps and more.

Spend a day at the seaside if the weather cooperates??
We left the Amsterdam crowds for an idyllic day at Waasenaarse Slag -- near The Hague-- and enjoyed the beautiful sand, warm-ish water, and beachside cafes. I was with a former local who had lived in Waasenaarse; I'm sure there are plenty of similar beaches.

In Amsterdam, don't miss the Resistance Museum.
It doesn't take forever to tour and it's really thought-provoking, highlighting the 3 choices that faced the Dutch (and any other people in a similar situation): actively resist the Nazis, actively collaborate with the Nazis, or adapt and try to survive.

Have fun planning!

Richard, I cycle all through S. Holland and I'd recommend using Strava. It's a fantastic resource and the "Route Builder" can put together some great rides. Also, you can piggyback on other rider's routes! The Netherlands is an amazing place to ride. It's quite flat - just be aware of the wind direction as it can often blow at 30-35km.