I visited Paris and Manon's flat with my 5-year-old son. We had a great time! Manon's flat had everything we needed. I especially enjoyed the separate bedroom, so I could relax in the living area at night without disturbing my son's sleep. Before our arrival Manon provided every information - location, getting there, wifi,... - I needed, and detailed too!
Manon's flat is in a very lively neighbourhood and at times I felt a little uncomfortable, especially later in the evening. But I never encoutered any problems!
I think the flas is ideally located if you are arriving/departing Paris through nearby Gare du Nord. Most of the major tourist sites are accessible by metro. The Sacré Coeur and Montmartre are within walking distance.