Hondarribia is lovely. North coast, really close to France (you can hop on a ferry across), lovely town centre with great pedestrianised square with loads of bars and restaurants. The beaches are great and there is one that is fab for kids as it has a breakwater which makes it v calm. There are kids clubs and things to do on the beach.
If you have a car there are loads of great day trips in driving distance: Biarritz, St Jean de Luz, the foothills of the Pyrenees, San Sebastián. Even Pamplona and Bayonne are close enough to visit.
Zarautz close to San Sebastián (Donostia) has a beautiful beach, great festivals and a nice local campsite on the hills. Lovely, lovely food there and especially in Getaria (next village). There's also a lovely beach and incredible old town there but less in the way of accommodation.