All of mine profess to believe ~ more I suspect out of fear that if they don't their stockings may be empty on the day than any real belief. The eldest confided, when she was about 6, that she knew there was no such person but she didn't want to tell Mummy 'cos "Mummy thinks there is".
Bless 'em ...... let them believe as long as possible ~ it's a bloody miserable enough world as it is and they grow up all too soon.