Every year the local ballet company takes over (for a week of Nutcracker), and they have about 150 or so kids that are running around.  But, they are the most organized group that comes here - with multiple parents assigned to each room/age group, meticulous checkin out procedures, etc.  While it can be scary to wander through - it truly is ORGANIZED chaos when they are here.  But, I worked a year once at a professional children's theatre - can't remember how big the biggest cast we had was, but it was entertaining.  And as the ASM, I spent a lot of time child wrangling.
-Centaura