This song is parents watching their kids newly married and very surprised how soon the years have flown by. They barely noticed they are getting older when they are already on their own.
This makes me notice of how little time parents have to influence and inspire their kids before they are parents themselves.
Seedlings turn overnight to sunflowers,
Blossoming even as we gaze
He is comparing seedlings and flowers to how soon his kids grew up! You seem to be there but then it seems you closed your eyes and they are all matured.