Last Sunday we went to the Parc de Torreblanca a great place to visit with kids just 15 minutes outside of Barcelona in Sant Joan Despí. On Sundays there is a little Farmers Market where you can buy fresh local products, mostly fruits and vegetables and not too far from the market are often creative activities organised for families with small children.
This family friendly park is huge and has several playgrounds, a labyrinth to discover and a small lake where my kids love to watch the turtle families and ducks that live there.
There is lots of space to play football and it is also ideal to ride a bike.
The ambience is really nice, lots of locals and many families, there is also a small café next to the Farmers Market where you can sit in the sun and watch the kids play.
The park can be accessed from four sides, though I recommend to look for the parking on Carrer de Torreblanca, it is a big free parking space on top of the park.
For further information please check:
http://www.elbaixllobregat.cat/parctorreblanca