I think you might find that all beaches on the costa brava are the same
we have been to all the resorts Lloret, fanals , tossa , malgrat , calella, s/susanna , pineda .
The beaches are not sand.

Estartit is probably the exception

Very gentle slope into the sea, best beach on the costa brava methinks

Thanks for your replys Cindermonster Estartit sounds good, do you know if we could get a train there?

You can get the train to Flaca and take a Taxi from there to L'Estartit or a cheaper option would be the Train to Gerona and take the Ampsa bus from stand 13 to L'Estartit (about 5 euros for the bus).

Accomodation is easy to find in L'Estartit so it might be worth your while taking a room for the night so you can get a full day there. I did a short break in 2000 while I was in Barcelona and walked into the first hotel I found and got a room.

Ampsa Website & timetable is http://www.ampsa.org/eng/serveis_regulars.html

btw, totally agree about L'Estartit beach, very gently slope, terrific sand and 5km long
Cheers

If you want to build sandcastles then the best beach is Estartit! I know this from experience with my kids. Fantastic 'sticky' sand that you can sculpt. Many other baches are shingle rather than sand.