"Are you doing well boys?"
les would not be used in a direct address, only in a discussion of third parties.
Why is it "les" garcons and not "des" garcons? They do not mention "the" in the sentence.
This should help.
There is a small blurb in the "Definite Articles" section about a noun in the general sense (e.g. "boys" instead of "the boys").
Hope that helps!