Make "git checkout" automatically update submodules?

Git submodules seem to be a great fit for one of our repos. The biggest pain point is that it's too easy to forget to update submodules.

1. I often forget since most repos don't need it.
2. Infrequent users of our repo almost never know to update submodules and
end up coming to us with strange build errors.
3. Existing scripts that work with Git repos are usually not built to handle
submodules.

In the common case of the submodule content having no local edits, it would be nice if "git checkout" automatically updated submodules [1]. If there are local edits, it could error out (maybe override with "--ignore-modified-submodules" or something).

I'm not a Git expert, though. Is there a reason something like this isn't already implemented? Maybe there's an existing write-up or mailing list thread I can read to get some background information?

Thanks!

[1] Our post-checkout procedure is:

    git submodule sync
    git submodule update --init
    git submodule foreach --recursive \
      'git submodule sync ; git submodule update --init'

(Not sure if this is correct. Different articles/blogs suggest a slightly different set of commands.)