lavandula

Your plan sounds good. For a map, go to Google Maps and enter "Place du Grand Sablon, Bruxelles, Région de Bruxelles-Capitale, Belgique" (or just Place du Grand Sablon, the rest will come up automatically). Zoom out (i.e. the minus sign) to get a handle on how it sits in relation to the Grand' Place (on this map it's in Flemish, 'Grote Markt'). It also marks the Musical Instrument Museum (Muziekinstrumentenmuseum). Place du Grand Sablon is not far away so you wouldn't need a bus. On the map 'Zavel' is Flemish for 'Sablon'.
There is apparently a view from the top of the musical instrument museum (I haven't visited inside it although I can say that the building is the most spectacular example of Art Nouveau, which almost got pulled down; thank goodness it survived). I don't know if you can see as far as the Atomium from there, as it's quite a way off.
It sounds like a nice way to spend the day, no pressure and lots of food (my kinda holiday).

Lavandula

iowamom

Great info here - we are planning 2 days/2 nights in Brussels with a side trip to Brugge with our 8yo DD (we've been to Brugge before) so this will really help us out!

yk

gidlaurie, all the places you listed are very close together and easy to walk to.

stardust

The musical instruments museum has a restaurant on the top floor with beautiful views over Brussels. So even if you decide to go for the Magritte Museum, you could still enjoy the view from the other museum. Both are on or near the Place Royale. From the Sablon, just walk along the rue de la Regence. As the name of the square indicates, you are around the corner of the Royal Palace, with a park in front. This could also be fun with your children if you have half an hour to spare.

http://www.musee-magritte-museum.be/
http://www.mim.be/
http://www.mim.be/the-restaurant

gidlaurie

Thanks again to everyone for your great insights. I do think the musical instrument museum will win out over Magritte (which would be my choice, but I am only one voice). I think I'll add the cocoa and chocolate museum to the list, too. I feel like I know so much more about this city now, as compared to the little I knew when I posted. Thank you everyone! This trip will only be later in the year but I will certainly post a mini-trip report when we return!