My oldest DD still swears that she saw santa the Christmas she was 6.
I had friends over after the kids went to bed Christmas Eve. My friends boyfriend had longer grey/white hair and had a beard to match. He was a little roly poly, and had on a red flannel shirt and black jeans.
I guess DD got up to use the bathroom and on her way back to bed, she caught a glimpse of him and went very quietly back to her bedroom. She didn't want Santa to think she was peeking, she didn't want him to take her presents taken away LOL
She truly believed in Santa for several more years, putting up with the teasing/taunts from other kids.
It kept the younger two believing longer too...along with waking them up to the sound of sleigh bells and reindeer hooves on the roof :wink: just before sunrise....