Him saying

is not boasting. It is entirely reasonable to assume that he's telling the truth here since that is far too artful a sentence for a 12 yo to come up with. Knowing his father's character, I'm sure we can deduce what Lucius views as a 'sensible line'.

Here he's boasting, he probably has no idea.

 

That means that what happened is Lucius literally said at some point "I think Durmstrang takes a far more sensible line that Hogwarts about the Dark Arts". All Draco is doing is parroting, he doesn't actually know anything about Durmstrang.

Which leads me to...assuming by Dark Arts he's referring to our old favourites the blood boiling curse, bone shattering curse and of course the Unforgivables. You don't teach them to kids...for one very simple reason, kids are cruel and also don't have any reasonable level of restraint.

In a country where gun laws are quite relaxed like the US, I'm sure many parents teach their kids how to use a gun, how to safely handle it etc. What they don't then do is let the kid carry it to school, where when they get in a fight they might just take it out a shoot someone.

Same logic here. Durmstrang might expose kids to the Dark Arts, maybe teach the theory etc But they won't be teaching them how to go around casting the Killing Curse at 11...