Why Parents Cry at Kindergarten?

I never thought of myself as a overly emotional person. Sometimes I'll catch a little tear fall when my kids do something great like finish a race in swimming, score a goal at soccer or shoot their first basket. But for some reason, the second I drove away from my daughter's first day of Kindergarten drop off, I was bawling. It was a full out sniffling, snorting, sob. My husband was in the car and I hate crying in front of him so I was trying to muffle it which only made it all worse.

Why did I do that? What made me so emotional? My daughter had been going to preschool since she was 3 and I had never reacted like that. What is so special about Kindergarten? Maybe it was how little she looked walking into that big school. Maybe I was feeling all the anticipation she was feeling and wanted to go through it for her. I don't know if it was the thought that she wasn't little anymore or that I no longer had a preschool child. Whatever caused that emotion was powerful and scary. I still haven't figured it out.