We stayed, a family of 2 +3 children, for 5 days in August. The apartment is wonderful ! Not big but well designed, maintained, clean, comfortable and mostly - located in the middle of all the most fun atractions in Madrid.
Sergio was very helpful and attentive long before we arrived (Incl. helping us checking in earlier than planed). There are great places to eat & drink and just under the apartment and at the near plaza.
We'll be happy to return to this lovely apartment with or without the children :-)