I need help my itinerary. We (husband and two teen girls) are flying into Barcelona in August and planned to stay three days. From there, I'm all over the place. I am trying to meet two sets of interest in the family--some like pretty beaches where they can swim and relax, do a bit of shopping; others like hiking and outdoor adventures. Here's what I have so far:
After Barcelona, we will rent a car and:

• Spend 4 days in either Tossa De Mar or San Sebastian/Biarattz. We don't need big cities so, the quieter (which I realize will be challenging!), more picturesque, the beach the better. Looking for a sandy beach that has some waves or is swim able. I am so torn between staying south or going north.
• Spend 2 days in Zaragoza. Is this the best choice? Looking for places to hike, some small villages.
• Spend 2 days in Madrid and fly out.

Any help appreciated!

My general rule is define the sort of beach you want.

Sandy?

Structured with services? Or wild and natural?

Easy to get to and likely very busy in August? Or something you'll need a car for?

Barcelona has beaches. They aren't blue lagoon tropical paradise but if you just want some sand they work.

I am looking for beaches that are different than beaches we have in New England. So hopefully warmer water and bluer water, places to swim, and not soooo crowded. I am fine moving away from Barcelona and towards southern France.
I’ve read a lot about San Sebastián and it seems like one large beach in a city, which is not really what I’m after. Biarattz seems like it might be nice?

Just north of Barcelona, look at Begur for beaches.

If you want warm water I'd point at the Med and not the Atlantic. Even better would be further south.

Anything easy to get to will be crowded in August.

I understand you mean Biarritz, in the French Basque Country. Just take into account that northern Spain and southwest France are quite rainy and beach weather is not always an option, so if looking for a sunny, warm area I would consider the Mediterranean instead of the Atlantic. Donostia-San Sebastian is a beautiful working city with three beaches, but do not expect any kind of a resort type of place or beach ammenities. Wonderful food, by the way.

You realise it is a five and a half hour drive to San Sebastian, on a good day? You could visit Zaragoza on the way there rather than doubling back.
Better yet if you stick to the Med beaches near Barcelona then you can take the train from Barcelona to Zaragoza and from Zaragoza to Madrid.

In only 1 week, I wouldn't go up to the Basque area.
August is high season and all well known beaches are somewhat crowded.
The less crowded one's may be in the Ebro Delta.
https://www.itinerannia.net/es/itinerarios/
There ae signmarked hiking trails from the French border up to Southern Catalunya.

Okay, thanks. Are there beaches near Barcelona (I was looking at Tossa De Mer) that are better than others?

Someone mentioned the islands and I'm not keen on taking a ferry over. Should we look near Valencia or Alicante area?

If you want to go to Zaragoza as well then you do not want to go down to Valencia.
HappyTrvlr has already suggested Begur up thread. Has the advantage of being not too far from Girona if the beach gets too boring.
Look at a map and look online to get a feel for some of the places not too far from Barcelona.
If you are happy to drop Zaragoza from your plans then you can get a train down to Valencia or Alicante area. You can then get a train to Madrid.

The Costa Brava has a gorgeous coastline. I was there too early in the season for beach weather, so I can't speak to crowds, but in addition to Tossa de Mar (which has the biggest expanse of a sandy beach that I saw in that area) and Begur (which has a lot of hiking trails), look at Llafranc and Pallafrugel.

If you like neither the beaches of Ebro Delta, nor those of Formentera, the next non crowded beach may be East of Almeria (Cabo de Gata Park).

lovely beaches north of Barcelona or south of Girona

You should go to Sitges! It's only about 45 minutes by local train from Barcelona, but has a very different vibe - SUCH a charming and quaint town, picturesque seaside, very blue and pretty waters, and super friendly people who live there. It's on the smaller side, but still does have some cute shops and delicious restaurants.