Okay, totally going to get hammered here, but.....
If it is causing your DCs this much heartbreak when they find out, why lie to them in the first place? I honestly don't get it.
My parents never told us about FC, Easter Bunny, etc. It did not kill the magic of Christmas at all! Or Easter. Christmas was a superexciting time for us as a family and still is (I'm 31
).
It was exciting because we knew our parents were creating special, secret surprises for us. We knew our dad hid the Easter eggs in the garden, but that just made it an exciting treasure hunt.
And it doesn't mean children can't appreciate the stories. This is what I never get: people wax lyrical about DCs' imaginations but then seem to think they need to believe FC etc are real in order to be excited. I never believed, but I still loved the FC story - I used to make my mum read 'The Night before Christmas' practically every evening from Oct to Xmas Day!
I don't have DCs yet but I think when I do I will tell them that these are special stories and make-believe that they can enjoy, but not that they are real and then have to reveal later that I have been lying :(