A family of actors is not an unusual thing. It's not what you know in this crazy biz - it's who you know, more often than not. Macaulay's dad Kit was an actor, as well as appearing a few times on Broadway, and so was his aunt, Bonnie Bedelia. She's had a few more roles than Kit - including in Die Hard and its sequel, which may explain how Macaulay got his foot in the door.
Within the Culkin family, the line hasn't stopped with Macaulay. Two of his brothers, Rory and Kieran, have also been in a few projects here and there. In fact, with movies like Signs, Scott Pilgrim Vs The World, and Igby Goes Down, and TV shows like Fargo, you could probably say that the brothers have been even more successful than Macaulay.