Some of the lyrics about Santa Claus go, He sees you when you're sleeping, he knows when you're awake, he knows when you've been bad or good, so be good for goodness sake. Telling children about Santa Claus encourages them to have better behavior, as bad behavior can, in their minds, result in loss of presents or lumps of coal.
There are some immediate advantages for children who believe in Santa Claus, and have those beliefs confirmed by their family. Many children enjoy the wondrous, magical feeling of the Christmas season, and enjoy the feeling that there is magic and generosity in the world that applies to all humanity. For parents it is also nice if there children believe enough to behave at all times to receive the gifts they want. However, when children do finally learn the truth about Santa Claus they learn valuable lessons about healthy cynicism and the way the world actually works, even if those lessons are painful at the time.
If we tell our children that Santa Claus is real, The tooth fairy is real, The Easter Bunny is real, it allows them to open their minds up to amazement and wonder. When they learn that we have lied to them and none of these supernatural beings exist, they close their minds to anything that can not be seen. So when we tell them that Jesus is real and that God exists, its no wonder they refuse to believe us. Children need to be taught the Truth, not fluff.
There is no sense in telling children that Santa Claus is real if they are eventually going to find out the truth when they get older. Plus, adults should not lie to children. It is okay, in my opinion, to tell kids about the real St. Nicholas and how people play pretend about Santa during the holidays.
I believe there is not a single good thing to come from telling children about Santa. By telling them to believe in the magical St Nicholas, we are teaching our children to believe and accept lies. We should be telling them who the real Saint Nicholas was, and if it follows a family's beliefs, what the real reason for Christmas is, Jesus. After believing in Santa for years, when the time comes to know the truth, some children could become heartbroken, and it could cause negative effects in the child.