We visited Berty's place for a long weekend with the two of us, to visit Rotterdam and North Sea Jazz. Our young children (2 and 6 years old) joined us for the last night. The location is great, right next to the Metro Station, at walking distance from the shopping center and the Markthallen. Parking is expensive but the (somewhat cheaper) Erasmus parking garage is at 5 minute walking distance.
The place itself is great! A stylish apartment which feels nicely spacious due to the high ceiling, two bedrooms and a simple, but proper kitchen and bathroom (with shower). You can hear some of the street's noises but it is not problematic. It is suitable to visit with kids although with young children (<4) you should be careful that they don't break stuff. Children's seat and baby/toddler bed are available.
Berty was quick in communication and flexible; she was not around during check-in but everything was taken care of. No problems there!
Altogether, a great place to stay and an excellent starting point for visiting Rotterdam!