They grow up too fast

I was thinking about how school changes everything about my life. I was so into the summer routine. The snack time, outside time, books and games were all at a nice routine that made my children happy and worked well for my schedule.
Now my son is in kindergarten all day and my daughter is in K4 every afternoon. I feel a little lost. I have 2 hours to work, clean & cook and I am a bit out of sorts. Did you ever feel like this?
It feels like they are growing up too fast and leaving me. I look at my daughter helping me in the kitchen and my heart stops, I want her to stay 4 forever. Since I'm an older mom I have friends with grown children. They say that the children do grow up too fast and that I should enjoy all of the attention, adoration and love that the littles ones give because when they are 16 they never talk to you.
I know that I wasn't the most delightful teenager ( It was the 70's) so I have nothing to complain about. I just have to hold these special moments with my little one's in my heart.