One of the unwritten rules of both teaching and parenthood is that we mustn't have favourites. Now, that's what I call idealism! In every other relationship of our life, we think it quite normal to prefer some human beings over others- we have best friends, a favourite aunt, a husband or wife for whom we might promise to 'forsake all others'- yet when it comes to children, whether our own offspring or our pupils, we are expected to miraculously feel the same about all of them.
What nonsense! Let's stop pretending right now, and deal with the fact that we often DON'T feel the same about all our kids.