So the Koopalings are not Bowser's kids. What are they then? Some possibilities: They're Bowser's bastards; Bowser Jr. is his only legitimate child and thus "officially" his only son. They're Bowser's nephews and niece that he has unexplained, indefinite custody of (like an evil version of Huey, Dewey and Louie). They're just a bunch regular Koopas who ascended to the top of Bowser's army due to their skill and loyalty to the crown. They're ruthless mercenaries employed by Bowser on the promise of innumerable riches if they can bring him Mario's head. They're a coven of warlocks, as evidenced by their proficiency with magic rods. They're a circus troupe (just look at Lemmy, he's an acrobat) that Bowser keeps around for his own amusement. They're a genetic engineering experiment gone wrong, a failed attempt to create a perfect Bowser clone. (Bowser Jr. is the first successful attempt, and thus the only one Bowser considers his "son".) Nobody knows; they come and go as they please, and may very well be older than the universe itself.