Overall we had a really enjoyable week with our 3 young kids (aged 6 to 10). The apartment (ground floor) is beautiful, spacious, has a garden. It is dated / old-fashioned, but in a nice, elegant literary way. Very well-stocked as lived-in, nice toiletteries and coffee supplied. The area of Brussels is a real delight, so many cafes and restaurants close by, and trams/buses every few minutes.
The only issue was the 2nd bedroom is in the basement. This basement is not accessible from the main apartment building, but down an outdoor stairs at the end of the garden. It's a grim basement, and we couldn't be so separate from our children. In the end, we didn't use the basement at all during our stay, but just used the spacious ground floor.