Our family of four, including a 4yo and a 1yo, loved this stylish apartment that is also very family-friendly. Suyeon was a most considerate host, not only providing a crib for the baby but also allowing us to stay a couple of hours beyond the checkout time so we didn't have to go to the airport too early. There are two separate bedrooms with doors - one of them comes with a small shower. There's also a third tatami room with futons and sliding doors that can close it off from the adjacent living room but not in a soundproof way. We used all three as bedrooms very effectively.
One very rare benefit of this apartment is that it has two toilets and two showers. There is a main bathroom with a toilet, shower and bathtub. Then there is another standalone toilet, and a standalone shower that is en suite to one of the bedrooms.
We also really liked the Sangenjaya neighborhood, which had lots of interesting little cafes and shops around the Chazawa-dori area. The apartment is about 10-15 min by bus to Shibuya station or two stops on the Den-en-toshi line by train. One stop down from Sangenjaya is Ikejiri-Ohashi, also worth exploring. For those with kids, Setagaya Park - about 15 min walk from the apartment - makes for a fantastic outing.
Definitely one of the best apartments we have stayed in within Tokyo. Thanks Suyeon for the great hospitality!