My parents never said he was real and they didn't push it when I knew he was fake. I did, however, get in trouble for telling other kids that he's fake.
Then one day I had a very short phase that he was in fact real, but that parents are his "little helpers" that he hires to hide the presents. No one told me this, I came up with it myself. Very brief phase during the tale-spinning "what if (random thing)?" part of my childhood, so I don't count it.