Danny DeVito and Rob McElhenney have been coworkers and friends for years. Morgan Lieberman/Getty ImagesRob McElhenney said he admires how his "Always Sunny" costar Danny DeVito has raised his kids.McElhenney said he learned that the key is to show up for his kids and be there for them. McElhenney shares two sons with his wife and costar Kaitlin Olson.Being a parent is hard.