Mr. Kelly is a true product of his era, a victim of the Great Depression. Unemployed because of an injury, Mr. Kelly has become the head of his family in name only. At the time, men were fully expected to be the breadwinners and, since Mr. Kelly no longer is, he doesn't have a clearly defined role in his family:
He was lonesome and he was an old man. Because none of the kids went to him for anything and because he didn't earn much money he felt like he was cut off from the family. And in his lonesomeness he wanted to be close to one of his kids – and they were all so busy that they didn't know it. He felt like he wasn't much real use to anybody. (2.1.16)
We just thought we'd throw you a major downer there, in case you were getting too content. (We wouldn't want that.) What makes matters worse is that Mr. Kelly seems like a really great guy, and he tries very hard to regain his footing in his family. It's obvious that he's a good dad, and even though Mick takes pity on him, he's just down on his luck.