We stayed for one week with our 2 year old daughter, in early September. The location was great. We walked everywhere (the beach, aquarium, sagrada familia, the zoo, design museum, big fun museum, museum of illusions, arc de triumph etc). Lots of cafes, restaurants and shops close by and public transport looked reliable and easy to access.
The apartment was on the 5th floor so required some forward planning getting the 3 of us, the buggy and the bags for the day in and out of the small lift but totally manageable.
The accommodation was clean and spacious. Great size bedrooms and living space. Fully equipped kitchen (we boiled spaghetti, fried bacon, had toast and cooked pizza without fuss). Towells were provided and a washing machine was in the bathroom, which was handy too. Loads of coat hangers, an airer and lots of storage space too. 4 little balconies, with shutters. On a main road but traffic noise was kept out by the double glazing. All in all we felt like we found the perfect accommodation for our Barcelona trip!