Well if you REALLY want to shut them up permanently, I think this response - in a very stern tone - would do the trick:
"Because we can't stand the little rug rats!!"
Seriously though - you don't owe anyone an explanation and if it's really terribly upsetting and annoying to have to go through this time and time again, I wouldn't hesitate to use the response above or something similar to it.. Some people just "don't get the message" without a little "shock" value..
"Because we can't stand the little rug rats!!"

Seriously though - you don't owe anyone an explanation and if it's really terribly upsetting and annoying to have to go through this time and time again, I wouldn't hesitate to use the response above or something similar to it.. Some people just "don't get the message" without a little "shock" value..