Kids...grow up so fast- let me say that again- SOOOO fast...I now have teenagers and can hardly believe it!  I don't think there is only one age that is worth photographing, I think ALL ages are.  They simply have many milestones in the first 20 years of life!  I love playing tag with them, seeing them laugh, then watching them run-out of breath and stop, only to find a calmness that is equally as beautiful.  Kids have the best expressions::  scrunchie noses, huge grins, missing teeth and big feelings that sometimes lead to tantrums with huge alligator tears and snot bubbles!  Bring on any age!