My mother assumed that because I was 9, I no longer believed in Santa. She called me from a department store to ask whether I'd read a certain Cherry Ames book she was buying me for Christmas, saying that since I knew Santa wasn't real it didn't matter if she asked me about the book.
I was shocked. I made super sure my kids believed in Santa. Then I told them when they asked at around age 7 or 8 if Santa was real, and I said yes, but he didn't bring presents to children who didn't believe in him. After that, I heard the kids talking about how they would check the handwriting on the gift tags that Christmas to see if it was mine. I ordered pre-printed gift tags for each child that year -- To X, Love Santa Claus -- they had a picture of Santa on them.
They were 13 and 14 when I finally had a family meeting and told them the truth. By then, of course, they had been pretending for years ... for me.