i knew from an early age that santa wasnt real, but i got a christmas stocking from santa till i left home....and i went home for christmas a few years ago for a few weeks and got a stocking then too.... my mum cant help herself
DD loved seeing santa at the shops and i have and will continue to explain it in a way that she will be able to make her own mindup....some people belive etc etc....i think its harmless and part of the joy and wonder of christmas and being a child, but i dont like the thought of using it as a tool to make a child behave...santa wont come if your bad etc.
i think you just have to explain it in a way were your kids understand that not every one belives the same thing, which is part of life anyway.