"You are not allowed to hook you sister." (the boys got pirate hooks to wear)
"Please do not be a bridge over your sister. Somebody's gonna get hurt."
"You are not allowed to practice thumping on your sister's head."
"No, you cannot sit with her in her chair...Do not be moving Button around in her chair....Ok no touching her or the chair for awhile."
"You picked a paper towel roll as your toy to bring?"
and my personal favorite...
"Okay, you guys can launch yourselves. Just aim low so you don't go through the window."