In "Flying Lessons," why has the grandmother brought Santosh to Europe?

In simplest term, Nani tells Santosh she brought him to Europe because he wins too many awards at school. What she means by this is that, while he is learning how to work hard, he is not learning how to live. As she goes on to tell him, when you are older no one will care how many awards you have won. They will care if you have something to talk about and if you never live life, you will never have anything to talk about. Taking him to Europe is an attempt to give him some actual experience of the world.