I left my then 6yo twice in the span of a couple of months. I had just adopted our second dd, so I had a newborn, 9 month old, 2yo, 6yo, 11yo, and 13yo. My two oldest boys usually put the 9mo and 2yo in their cars seats while I took care of the newborn. 6yo was responsible for getting himself in the van. Twice I drove off without him. We left him at a friends house and church, and immediately turned around to get him, so it wasn't too terribly scary. That's when I started doing a head count.