Wow, where did these actors come from? Throughout the film, I was in turmoil who was the better actor, Adele Haenel or Vincent Rottiers. She did an outstanding job in an almost non-speaking role and he was very morose, gloomy and violent as well. I do believe that to get children (although they're almost teens) to act this way is very hard. And to accomplish it in two actors, is very admirable. Ruggia did an excellent job, maybe the casting alone was 90 percent of that.
Without spoilering anything, I would like to comment that the let's say, 'least boring scenes' between Haenel and Rottiers, to use a heavy understatement, have not been shot in a mainstream film, since Maladolescenza (1977) ( http://us.imdb.com/title/tt0076749/ ). I suppose Ruggia didn't care about American distribution, and rightly so. Take into account that Maladolescenza was shot in a very different era, where a lot more was possible, a much more permissive epoque when not EVERY bit of skin was declared porn as it is now, we have to salute Ruggia even more, and Haenel and Rottiers as well. Although ... I don't know what the reason is that Haenel has not made a film since Les Diables, and Rottiers has. If it is because of those 'least boring scenes', then that surely would be a pity, because then we would have lost a potentially great actress.