We stayed at Sophie's place for 4 nights at the beginning of our family holiday this August, with our three children aged 7, 5 and 2. We loved it! My eldest son didn't want to leave Paris (even though we're going to the beach next).
The apartment was clean, very comfortable and well equipped as well as quirky and stylish. With three young children, it was really useful to have a fully equipped kitchen with all the basics available to cook in the evenings, wash their clothes etc. Everything you need is provided in the apartment and easy to use. There's a DVD player (although we only used it once as we were out a lot) and the children were delighted to discover the toy box. The four flights of spiral stairs did not bother us and the children treated them as part of the adventure and charged up them when we arrived (I was sure they would moan, but they didn't, even after climbing the Eiffel Tower).
Sophie was really organised and clear in her communication and helped us plan sleeping arrangements, parking etc. and arranged a host to meet and show us around the apartment. She leaves a pink folder which is a gold mine of detailed local information, maps and tips.
The local area is lively, interesting and well connected to transport networks and amenities. (Don't believe the review that says it is the 'red light district' -it's really not. There are various nightclubs and the odd sex shop plus it's near the Moulin Rouge but it's also full of cafes, shops, supermarkets, bakeries, restaurants etc.). We walked to the Sacre Coeur with our children from the apartment with ease, and went all over Paris on the Metro as well as a day trip to Disneyland. The children particularly enjoyed the waffles from the vendor on rue des Martyrs which Sophie recommended. We really had a great time and are hoping we can stay at Sophie's the next time we visit Paris.