Lol at Jooly, I do that too (well, I mutter it under my breath!! ). Please and thank you very important, although I don't remind visiting children.
This thread reminded me of a really sweet incidence at a kids' party, mostly 4 and 5 year olds. The magician started to do his first trick, waved his wand and asked the kids "what are the magic words?" One little boy put his hand up and said "please and thank you!!" All the mums went "aaahh!!"