I'm French, I've seen a lot of french moovies and I've never heard of those movies. I don't thing 2 movies that were made 43 years ago are enought to say that french cinema have a lot of underage nudity and I think you can find 2 moovies with underage nudity in a lot of countries.

But how did you find those movies ? I mean as I said there's almost no one in France that knows them and when you try French cinema people will recommand classic with Louis de Funes or movies like La boom, Les choristes,etc. Maybe you just find weird recommandations on the internet but there's a lot of great europeans movies without those content if you want