My wife and I and our daughter recently stayed here while on a week-long trip to Oslo. I would highly recommend this apartment for a couple with a single child.
The apartment itself is lovely. It's nicely laid out with large windows that let in a lot of light. It has everything that makes an apartment so much more enjoyable than a hotel, such as a nice kitchen and washer and dryer. And our daughter loved her room.
It's very well situated, as well, right next to Frognerpark but with easy bus and tram access to the rest of city and a good selection of stores, cafes and restaurants in easy walking distance.
The host was very responsive to any questions we had and check-in and check-out were very smooth.
I don't think we would hesitate to stay here again and would recommend this to anyone else visiting Oslo.