My son's best friend is Jewish and tells him there is no Santa Claus. How should I handle this?

My 6-year-old son has a best friend who’s Jewish. And this best friend has, over the past several weeks, been going around telling some of the kids in their first grade class that there’s no such thing as Santa. My kid still believes – very much — in Santa! And I’m not ready to shatter the illusion.

What recourse do I have? Can I call the teacher? Can I talk to the best friend’s parents?

— Believer