Hm... Getting to know 'em one at a time is a good idea.
If I was in that situation, that's prolly what I would do. Granted, me being me, I'd ask 'em to go to the bars for an evening, have some beers & wings, play some pool, and the like. (Sadly it's sometimes interpreted as a date when I do that... though the guys seem rather taken aback when I drink more than they do and then beat them in pool... if they learn I'm not interested in guys anyways, they tend to back off; I've made a few friends that way.) Don't know how that would work in your situation, though; is hanging out after hours with co-workers common at your workplace?
Also, you say "young men"... if there's a significant age difference between you & them, that may also be a reason why they scamper off & stop joking when you come around. They might see you as in some sort of position of higher authority (or perhaps just someone who would be bothered by joking & apt to tell management), even if you're not technically their superior. *Shrug* maybe try throwing in a joke once in a while... they might be taken aback at first, but showing some wit--or mostly just showing that you can handle joking--may be helpful.