Nit Picks on Au Revoir les enfants

Rating: Null/10 (23 March 2007)

The movie is fantastic. I have just seen it for the first time as it is running this month on FLIX. After having watched it several times, there are somethings which while probably minor do confuse me. Perhaps others have the answers.
1. Getting right to the ending of the movie, it is implied that Joseph was the snitch who put the Gestapo on the case. Yet from what I can see the only person who knew Bonnet was Jewish and his real name (other than some in the school administration of course) was Julien. It is pretty obvious Julien managed to keep the secret...his brother had no idea nor did his mom who told him his friend is very nice. How then did Joseph know there were Jewish boys being hidden in the school (I suppose maybe one of the others figured it out from the other 2 but of course nothing in the movie talks to this).
2. In a similar vein, why would a smart kid like Jean Bonnet keep his real name with him in some of his belongings and why would the headmaster have the information to give the Gestapo guy Dr.(?) Muller the real name of at least one of the boys namely Jean.
3. Here is also a puzzle. In the last scene in the infirmary, one of the German soldiers uses the pull down your pants test to ascertain whether Julien is Jewish (either he passed or they found the other boy before the test was completed)...but my question involves this...if it was very uncommon for non Jewish boys to give up part of their equipment very early in childhood, wouldn't they have noticed that Jean and the other boys were missing part of theirs. I find it hard to believe that during a two week period of close quarter living in dormitories and a visit to a public bath, none of these boys saw the others au natural so to speak. Wouldn't that have been a tip off?
4. Finally the movie takes place during a two period in January 1944 notterribly far from Paris...I was in Paris this past January and while it wasn't terribly cold, it certainly wasn't really spring like either and it is evidently cool if not bone chilling during the period of time the movie was filmed. So my question is why were the boys always wearing shorts....was this the uniform required of catholic school boarding school boys in France? Seems not to make sense to me.
Despite these questions, the movie is fantastic and everybody should see it; even if they know the ending.