On this topic I just had to tell this story-- my little brother is 3.5 and I had to use the bathroom for almost the entire class, but hate public restrooms and was trying to wait. The what I thought was a 45-min. class was running to 50, and I thought perhaps I had the time wrong and had the ten minutes to run to the bathroom. Even if the class had ended right that second, I would have at least a few minutes because of little brother's "ladies first" stamp and water policy. I left my keys in his cubby with his shoes so he knew I'd be coming back, and headed for the bathroom.
Between finding the bathroom at the new gym/sport complex thing and the broken toilet causing a little line, I must have taken longer than I planned to. When I got back, I found my brother sitting at a table in the snack area, shoes on, "reading" his handout. When I sat down at the table with him, he informed me that I had "forgotten" my keys in his cubby. And "Can I have a pretzel I was listening today!" If I had taken any longer he probably would have used the keys to drive home!
After a slight coronary from considering what could have happened to this little boy in a public place by himself, I figured that while he was probably ready to be left during class time, I sure wasn't ready to leave him.