Think from your childhood.
Instead of thinking from a mom's point of view. Step back and think about when you found out Santa wasn't real.
How did it make you feel?
Were you upset that your parents lied to you?
Were you mad and hurt over it?
For me, I was a little disappointed because all that time Santa brought me everything that I had asked for but when Santa didn't come one morning. I thought things like "Was I not good this year?" "What did I do wrong?" But when my mom explained to me what Santa was really all about and how I could help spread the holiday cheer by being 'santa' for a younger cousin it made me feel wonderful because they wouldn't know it was from me but it would be exactly what they wanted. Everyone is different though so I don't know how everybody will react to the news that Santa isn't real.
Here's another question. At what age do you tell your children that Santa isn't real?