Who's taller?

I think it's funny that 6 of my kids are almost the same 3 heights.  Nathan and Michael are about the same height and I think Michael might be a slight bit taller than Nathan.  (See the pic below to see how happy he is about that.)  Anna and Katie (although Anna's passing her up fast, lately).  And Lydia and Elizabeth.  I predict Lydia will always be short like her mommy.