First - the location of the flat could not be much better! We have been in Paris quite many times, but Montmartre and this area is best. Lot´s of bistros, restaurants, grocery shops, excellent vibe (not over touristy).
Flat is of course not too big, but also not too small, for small family 100% OK. BUT - the terrace compensates it all. Small green secret garden.
Flat is super clean, beds are comfy. If You close the window shutters it comes bit dark, but this is not big issue. And also - as You are in the middle of life there will be some (not much) noise from late people :-)
Overall - 100% recommendation.
All the best,
Erkki