Most children realize on their own about Santa as they get older. Children generally start to figure out that a parent or other adult is Santa as they get into elementary school. Their logical thinking skills are developed enough by then to let them realize a white bearded man can’t travel through the sky in a sleigh pulled by reindeer to every home in one night.

From articles.cnn.com

-quote
The important thing is to take your cues from the child, and not try to prolong the fantasy for your own enjoyment when they may be ready to give it up.

Follow your childs (child’s {sic}) lead
-endquote

When your daughter raises doubts about Santa, the best way to tackle the subject is to say that while the legend of Santa isn’t true, the historical facts are. There were historical figures who dressed up and brought gifts to children in their homes. The spirit of this giving is not a myth.

If you are Christian, you can also tell your daughter that the three wise men started this tradition of bringing gifts to children.

As soon as your kid can begin to understand about the fictional character of Santa Claus, you can talk to him about this world-famous Christmas character. Children can begin to wonder about who he is when they see his impersonators outside. The burly man with white, long, and curly hair loves to bring joy during the holiday season. He loves to give presents to children and carry them on their laps.

In talking to them about Santa Claus, they want to know where he comes from, how his family is like, and how he began. You can read to them a story about Santa Claus. Through it, they can know more about him and appreciate the idea behind Christmas better. He is a unique character created for their happiness and imagination.