For my daughter:
If your friend comes over today, please keep at least 30 feet distance from the boys at all times. At that distance it's very difficult for them to throw things accurately.
Please leave them alone, and don't antagonize them! School is starting soon, and you won't be able to achieve perfect attention if you are dead or dismembered.
For my sons:
If your sister's friend comes today, BE PERFECT GENTLEMEN.
When I come home I expect to find there's been no bloodshed. But should this become necessary, please make sure to do it outside, so it can be hosed off.