We loved our trip to Valencia, the flat is in an excellent location. Being so close to the beach front, only 10 min walking; and with the 19 bus (€1,50) around the corner takes you into the city centre (in 30min) or the metro station Maritim at walking distance, only 12 min (€2) that takes you down from the Airport.
It is also handy to download a taxi app: Cabify or mytaxi, it worked well for us for a 20 min ride €12. The airpot ride showed up at around €25 but we used the metro instead for €2 each (kids go free)
At the flat there is no kettle or working WIFI (we didn't need it so we didn't complained about it, but given that there is a code to sing into the WIFI, we expected to work)
For us the mattress is too hard, and the pillows too high, but that is very much personal, we managed using one of the pillows from the kids bedroom.
The main issue was the noise from the streets, as the flat is only on the firs floor and there is not double glassing, so during the weekend and early mornings it is constant and unbearable (for us), and difficult to go back to sleep.
That was the reason we didn't relax as we were expecting so.
We have a 6 years old daughter who loved her bunked bed, and enjoyed every bit of the trip, the walks, the beach, and in the flat watching tv.
The neighbourhood is busy, lots of tourists and locals at all times, and it looked safe.
The are plenty and for all tastes local cafes and restaurants, the food and coffee in Valencia is something that did not let us down!!
We can recommend Las Carabelas (beach front restaurant) for Paella Valenciana -it is only at lunch time and do book before hand. I would not recommend CA LA MAR or the Italian Estrella de Mar at the corner of the flat. Try Pannes for breakfast, and to Los Olivares for ice cream. Plus theres is a supermarket Mercadona around the corner where you can pack up the fridge with water (I don't know if you can drink the water from the tap), breakfast for the little one, ice cream, and the basics to survive your time at the flat and fix something for lunch at the beach.