Suitable surf spot
If you are going to South West France you can expect more powerful waves than Cornwall and I would not really recommend anywhere like Hossegor for a beginner. You would be better off to go on to Biarritz where I would suggest that Cote des Basques beach would be the most suitable spot for your son to progress. This is a more gently sloping beach, providing a more mellow wave than most places around. Tuition is also possible there. It is one of many Biarritz beaches and the area is really beautiful, with the mountains (Pyrenees) nearby and lots going on in the town, great restaurants, etc. There are a number of different breaks within a short distance, and even if he is not yet up to experiencing them, there are beach breaks (eg Grande Plage), reef breaks (eg Guetheray) and even a point break (Lafitenia) to check out and watch the action. It's only a short drive to Spain, too, if you feel like a change of scene. Like anywhere in France though, Biarritz will be very crowded, especially in August. Bon Voyage!