Hi Vicky
Tossa's a great little place. I'm sure you won't be disappointed.
Barcelona is a must. There are buses direct from Tossa every couple of hours. But it might be easier, and you'd see more, if you took a guided tour. There's a travel agency about halfway up the main drag (walking away from sea) on the left. They do good tours with English speaking guides (often actually English) that take in most of the main sights in a stress-free manner.
The nearest water park is at Lloret -
http://www.waterworld.es. I haven't been as I tend to go out of season, but have heard many people say it's good, and very big.
Beaches in Tossa are OK, though very coarse sand - take your surf shoes. The sea shelves very steeply so it's not so good for non-swimmers. I prefer the little beach at the north end of the bay - Mar Menuda. It's got a shallow sort of natural pool that's great for kids.
There are better beaches nearby: Canyelles, half way to Lloret, is very pleasant and has a nice cafe; Giverola, about three miles north, is very pretty, and easily reached on the glass-bottomed boat that goes from Tossa.
Another good day out is to take one of the scheduled passenger ferry boats to Blanes. It's a resort and a working town and port. There's a market along the seafront on, I think, Mondays. More interesting is the produce market on the street that runs parallel to the seafront, one block back. And that street has a superb, atmospheric, cheap tapas restaurant called Las Terrassias, or something similar.
There are plenty of good restaurants in Tossa. The ones along the front, particularly towards the old town, are a bit pricy, but you always pay for the view. Have a Google and a look at Holidays Uncovered and other websites.
Have fun!
- Tony -