FWIW, we never told any of our kids. Our daughter (6) still believes. DS10 and DS8 figured it out together a couple years ago. Neither of them felt lied to or anything negative; they were more bummed out that it was true.

Also FWIW, I figured it out when I was 7 or 8, and I never felt lied to. For me, figuring it out was just part of growing up.

Val