Why must they grow?

We are switching to winter clothes at our house today.  The girls are "shopping" in our living room from the many bins of clothing we keep in our garage.  They LOVE it.   So, while I'm watching them try on even bigger (which really equates to longer) clothes than I expected, Jeff pulled out the tape measure and started seeing how much they really have grown.  Ashley is 4 feet 6 inches.  Alona is 4 feet 4 inches (I'm pretty sure one of these days she will pass Ashley in height).  Natalie is 3 feet 8 inches.  Natalie is the most surprising- as she is only 4 yet has to wear size 6 pants for length.  They are all growing up way too fast!