someone I know has a 3 year old, this Christmas was the first she really go the whole 'Santa' thing so the parents played along with numerous trips to see Santa a 'Santa Stop Here' sign etc.
Today was the first time I've seen her since Christmas so I said did your DD enjoy Christmas and she said "She did but I was getting a bit pissed off with Santa getting all the credit for the presents after I chose them, bought them, wrapped them so I told her Santa wasn't real and wasn't mummy clever for getting all the toys"
AIBU to think you either play along with Santa or if you object to the idea tell your kids from the start. Not play along until you get jealous of Santa!