Maybe it's because Americans treasure the ritual and rites of a wedding that we tend to pay a lot more attention to First Daughters than First Sons. Who can even remember President Ford's son's name, even though we didn't miss one news item about daughter Susan, who went on to marry her bodyguard?
The first famous First Daughter and one of the first American celebrities had been Alice Roosevelt. An independent female who liked the color blue she was responsible for "Alice blue" fashions. The next daughter to capture our full attention had been Sweet Caroline, in the short-lived Kennedy Administration. For years we worried how the murder of her father would affect her. Then there were so many other tragedies to visit her that, well, we sort of drifted away. As T.S. Eliot observed, human beings can't absorb too much reality.
The Johnson First Daughters and later the two Nixon ones were forgettable, but not soon enough. Amy Carter's tenure in the White House was short and since her father seemed to be screwing up the economy and lots of other things, we had to turn our eyes away from that whole scene. Old-man Ronald Reagan arrived after his zany bunch of kids had already grown up. Chelsea Clinton was kept hidden so we really didn't have the opportunity to bond. The Bush twins, a fun pair, were a delight. We hoped that they would never fully grow up.
The Obama two girls have been flawless in their performance art. The only better act in the White House is that of the dog and Mama Bear's dresses.
In 2016, if Hillary Clinton wins the White House there will be no First Daughter, only perhaps a First Husband. That new category will provide endless entertainment.