Agree with all previous reviews: Koen's place is amazing for families.
Location is great - away from the "tourist" area and yet less than 10 mins from Luxemburg / Mouffetard / Pantheon; with plenty of transport (RER /buses) and food options.
The apartment is very pleasant and equipped - although it has only one toilet and 2 separated baths. Internet connection was very unstable and unreliable - it should be essential as water nowadays. Anything else was better than expected.