Holiday Characters Taken Seriously?

Now we all know the typical characters like Santa Clause, the Easter Bunny etc...most of their stories are cutesy and fun because they are intended for children.  In the new movie Rise of the Guardians they are anything but cutesy. (1) They are taken seriously. (2) They are modernizing these characters in a very real way.  No stupid gags or anything like that.(3)  This movie is also showing kids, according to Peter Ramsey, "it's okay for kids to be afraid.  Its okay for them to know there is bad in the world and someone out there is going to protect them from it".  I think this is a great approach.  Also the way this movie takes story boarding to a whole new level to add another layer into the movie is cool.  I never thought like that.  For my final question...what is world-building?  I have a general idea from the article but every time I read that word I keep going back to movies like Inception.