I'm seeing a lot of judgement on pretending Santa exists vs being 100% truthful with your kids. I don't think either way is a bad way, but don't judge others if they choose to pretend Santa is real.
With that being said, I do agree that if you are going to go with the Santa story, when the kid asks if they are real you should be truthful.
I just went through this with my 9 year old. She just came up one day and asked me if Santa was real and I told her no. There were a lot of follow up questions and it made her realize the tooth fairy, Easter Bunny, etc were the same situation. She asked me why we pretended Santa was real and I explained for us it was nice to see the magic that they felt from a stranger being kind just for kindness sake.
For me personally, I think it's a good lesson for kids to begin logically questioning their world and what they've been told.