When my son was 3 we hadn't really taught him much about Christmas and Santa yet. We worked late and as a good behavior reward, we stopped to get a doughnut - it was the only thing open at 10 pm. The doughnut lady asked DS if he was waiting for Santa to come and bring him presents. He didn't know what that was about. We explained some on the way home but it was late and we were tired. Got home and put him to bed. 3 hours later he is SSSOOOO NOT asleep. So I asked him what he was doing. He said he was waiting for Santa to show up. We told him to get some sleep... not a time to explain anything to a 3 year old... right? Well, he's still in there an hour later bouncing off the walls so to speak. DH got up and put a pillow in his red pajamas and pulled a stocking cap over his hair and put some quilt batting around his face and went in the DSs room and told him Santa was here and he better get some sleep right soon. Well, the next morning he gets up bright and early and he says, "Mom, don't tell, Dad but I know who Santa is." I just winked and said that would be our little secret.