person A: I'm sad. My youngest son starts kindergarten tomorrow!
person B: I am sure it is a bittersweet moment.  I can relate myself.  It takes some getting used to
person A: I mean i'm happy for the up coming peace and quiet but it's still sad all my kids aren't babies anymore.
person B: You will still have plenty of time before your son becomes an unruly teenager.  Cherish it.
person A: I've got a 12 year old that's getting mighty close!