Just to start, I have a 15 months daughter, and our host Cristina, knowing about it, received us with a set of crayola pencils and a notebook for her to paint. That already made me confident we were in front of a kind and professional host that we could count on. She also gave us a lot of information about Barcelona regarding public transportation, supermarkets, areas to visit and so on. We were there to look for a long rental apartment since we are moving to BCN in the summer, and she provided us with good advice about the city areas that are more suitable for a small family. She also gave us a heads up about the subway strike there was in the city that day, and that we were not aware of at all.
The apartment was beyond clean. A rather small apartment yet spacious and well arranged with two rooms and a terrace where we could enjoy some red wine in the evening. We found it perfect for the three of us, and certainly four people would be very comfortable in there. It is in the city center, five minutes from the Sagrada Familia (Gaudi's Cathedral). Now, be aware you are in front of the Diagonal, which means constant traffic during the day, so don't plan to sleep during the sun light hours. At night, it gets very quiet. We walked everywhere from there, and it was nice to do so. Cabs are passing by constantly in front of the apartment door.
To summarize, we are certainly very pleased we chose Cristina and Clara's place.