Tagging svn:externals

[C M]

It seems that SVN does not tag svn:externals.

We have defined a structure such that child projects have link from a
parent project.

Parent project -> child project_1
                      -> child project_2
                      -> child project_3

However, when you go to tag a release for a child, there's nothing in the
/tags/Rel_X as I would normally expect.

What's going on here?
Amad