I think S ranks are fine, since lots of games before this one basically have them, but the system needs to change. Characters need less S supports and more opposite gender friend ship supports. If everyone only had like 3 romantic supports I think it'd be a much better system overall.
But children are worthless. Unless they are a part of the game, like FE4 or Awakening, they should not be there. The excuse in If is awful, and they're just thrust into the game.
As for class restrictions, who cares? Having more options for characters is interesting, and it opens up the possibility of buff females like Rinka, and who can say no to that?