We stayed one week with 2kids (0 and 3).
Good points:
• Super location. We didn't need to use any metro/bus to get to all the sights in Madrid.
• Many restaurants, bakery, Cafes and supermarket are just around the corner.
• Smooth communication. Luis and his son were helping us with the luggage for check in and out. We could leave our luggage at Luis's office. Very kind host.
• Very well equipped kitchen including essential seasonings. Towels were fantastic.
Negative points
• Beds for us were bit too small. the bed size was about 140cm and for me and my daughter to sleep in was really narrow.
• Apartment looked bit older and smaller than what we thought on the photo. (but high ceiling and location compensate
the negative points in my oponion)