As little ones become older, photos become a memory.
Capturing memories at every session is the best part and also a sad part. Yes it the best part because these are photos that they will look at in future years. However, this is so sad, due to the fact that these will be just fond memories. Memories that they may miss the little ones being so little. 
Maybe the children are older in high school, no longer has time to give their parents a hug anymore. The parents will reflect on these memories and remember how their little ones would scrape their knees and run to mommy & daddy begging for a hug to make them feel better.