I have a couple of lyx documents (the children), I want to create a master document that referencing the children, but if I use Insert -> File -> Doc Lyx the file is copied inside the master document, but if I change the original document (a child) the change is not reflected in the master.
Maybe it is not posible?
Go to Insert > File > Child Document. Then click on "Browse". Then choose your LyX file. Then choose between "include" and "input".