There is an excellent one halfway between a little village called Bidart and Biarritz itself called Résidence des Pins (campingdespins.com). We went there last year with Eurocamp (eurocamp.co.uk). Although it's busy in the summer, the campsite is really good for families with a children's pool and an on-site children's entertainer. And there's a beach within easy walking distance.
Elizabeth Kerfoot

I'd recommend Cap de l'Homy (600 Avenue de l'océan, Lit et Mixe, 0033 5 5842 8347, camping-cap .com), up the coast towards Bordeaux. It is a fantastic site under pine trees just on the other side of the sand dunes from the sea.
Lucy Harding