Dear Parents and Children Frequenting the Library,
The library is not a baby sitting service. If you trust that your children will behave if they are left alone in the library, that is fine. If you want to drop off your children while you do other things, or have them come hang out at the library after school until you can come get them, and they cannot behave, that is not cool.
The library is not a playground. True, some libraries have some playground-type equipment in the children's department, but that equipment is contained within a certain area. It is not appropriate to play tag or hide-n-seek throughout the entiriety of the library.
These things tend to make me smashy, so if you don't want a heavy book flung at you from behind the counter, I suggest you get your act together.
Thanks and have a good day.