We (a family with 2 kids aged 9 and 11) stayed in Javier's apartment for a citytrip.
It's well-situated because it's close to the beach, all kinds of restaurants and the city as well as an underground/ metro-station.
Despite this it's very quiet so we slept well in the apartment which was very clean. The kitchen is big well-equiped so if you choose to cook it's easily managed.
The apartment was airconditioned which is great in summer and the WiFi was really good; something the kids were happy with after 2 weeks on a campingsite without WiFi 😉
Very good place to stay if you go on a citytrip. And Barcelona is also great with kids.