Hmm, I can understand both sides of this. On one hand, it can be considered lying to your children, on the other, it can be used to ignite the imagination of children and create special childhood memories. Personally, I grew up believing in Santa Clause, Tooth Fairy, etc as a child. I look back fondly on those memories as a kid and it makes my childhood seem more magical because of it. On the flip side, I was also told the true meanings behind the holidays we celebrated and understood that the true meaning was more important than the fun stories of Santa or the Easter Bunny.
Overall, I think every parent needs to follow what they feel should be taught to their children. I think a person can teach their children about these fictional stories, but also teach them the true stories of why we celebrate Christmas, Easter, etc.