The flat is more than great for a family with kids for a relaxing stay in Rotterdam. Kralingen, the district itself is very calm, there are playgrounds and child-friendly restaurants nearby, where you can begin or end your day. Anyway you can easily get into the city center in 15 minutes by metro/tram.
The flat itself is very comfortable, very stylish, with all the equipments you need for a baby and for a relaxing stay when the child is asleep :) (balcony, wine, books, dvds, music cds). The breakfast is great as well.
All in all you can feel the care of the host, Betty. She is really making a good job! Thanks!