I walked to school, and over to friends houses when I was in elementary and junior high, but when I was in HS almost everyone (except me) was bussed in. My kids could have walked on their own a few places, but mostly they were with me until the oldest one could drive.
When they started riding and doing combined training, I found that I couldn't watch them out on cross country. Most of the photos that I tried to take of them jumping, actually turned out to be of the ground or the sky or something. I think I shut my eyes.
The hardest thing I ever did though was to let dd#2 walk off at the Air Force Academy for plebe year. She wasn't allowed to have any civilian clothes or to phone home for 6 weeks. It was just like cross country, except she didn't come back (until Christmas break)
I'm watching pre-season football, and John Madden has just said that the mother's of quarterbacks have the worst of it. The players themselves are concentrating on what they are doing. But the parents just have to sit there and watch their boys get hit.