Children believe in Santa - healthy or unhealthy
Believe in something that is a myth but based on a story of a man who gave gifts to the poor. Then there's the fact that its Jesus's birthday and you celebrate with gifts because he shares his love. I think that it's okay to let your kids have a healthy imagination as long as they learn the real story behind what this day represents. Santa is a helper to deliver gifts of love and joy. I'm for Santa but I write on the gifts from mom & dad.
It's your choice to tell your children what you want to. Just remember that "Christmas" is a day to keep peace, love and joy!