It is a common theme in One Piece, but before I go on, no this is not about the main characters, for example Luffy, and another example Ace. Or even part of the SH crew, this is about Family in general, including them. I love how Oda makes this a central theme, most recently with Kinemon and Momonosuke. It was a theme with Sabo and his parents, Nico Robin and her mother, Usopp and his father, Luffy and Dragon, Ace and Gol D. Roger. It is common indeed, it is about this theme as a leitmotif in the series and the meaning behind it.
Family in general is portrayed by Od by being in danger. Before the WB war many families were praying and stuff, recently with the whole kids on PH and the parents crying to the marines. On Fishman Island the small children asking Madam Shirley about what will happen. Also the way Oda focused on the family on Fishamn Island when the crew was exploring it.
Even though Fathers are dominant figures even in the world of One Piece, what does Oda symbolize with the many family relationships, focusing on children as well. For example the CP9 were orphans, trained by the government. So for Oda the government is a threat to the common family? And to the children as well? Is this why this theme is present, to represent that strong family bonds may hold people up in a crazy and upside down world like the one the people in the One Piece universe are living in? Discuss more, i am eager for everyone's opinions.