We are a family of 4 giving our little nest for a rent when travelling. There are 2 bedrooms and a living room - that makes around 60 sq m.
Ours kids are 1 and 2,5 years old, so the apartment is ideally equipped to host little investigators (beds, toys, baby chair, baby cook, even a stroller if you need one).
But let me add that the apartment is great for a couple without kids as well. The children stuff stays in their bedroom, so the apartment is all yours ;)
Enjoy Paris :)