KFB, you ask “What if their parents are broke or they don’t think they should support their kid who isn’t working?”
Those are two radically different things. Being “broke” is something for a beis din to determine, and if it’s so then the community needs to step in. “Not thinking that they should support their kid” is a huge misunderstanding. It’s Torah we are supposed to support, not a “kid who isn’t working.” The kid is presumably working hard, at Torah. If he isn’t, his rosh yeshiva needs to step in. Either way, no one (the medina, the parents) should be able to dump avreichim into the street just so.