The usual disclaimer: This being 40k, different sources will say different things. They are all equally valid (as would be the stuff that you make up for yourself); contradictions merely present different options to cherrypick from. My own interpretation draws heavily from GW's own material, which in spite of it officially not being any more important than some novel or FFG's stuff, I still view as a sort of common ground between fans.
With that out of the way ...
Indeed I do believe in civilian trains following Guard regiments around, very much like it was done for the armies of the Napoleonic era. The reason for this is that the organisation of a regiment, as explained in GW's material, is 100% combat troops, with no elements set aside for logistics duties as is common in modern armies nowadays. Additionally, the background for Whiteshields specifically points out that the children of Guardsmen are "usually brought up completely within the regiment itself" as it "acts as a kind of extended family, infusing the youngsters with the culture of the homeworld they have never seen, and assigning them menial and support duties which would otherwise eat into the regiment's fighting strength". This, to me, means that (1) yes, Guardsmen get to procreate during their lengthy tour of service and (2) there must be someone following the regiment around, caring for the children for as long as they are still too young, and probably taking over a variety of other duties.
Whilst probably less efficient than a trained logistics corps, this unified approach makes sure that a regiment of feral warriors will be organised along similar lines as one from a civilised world. Additionally, given the lifestyle of the Imperial citizenry in the 41st millennium, it stands to reason that even those civilian camp followers will be able to withstand the hardships of a military campaign, unlike as if you'd grab a random civilian off the streets in our modern world. After all, those camp followers are the same kind of people that make up the gangs in the underhive, or the mutant-purging militias of the Ministorum.
The exact composition and nature of these trains will probably differ from regiment to regiment - with some having merchants, relatives and servants signing up right when the regiment is formed, whereas on other occasions the soldiers may forcibly conscript labourers from the population of the world they are fighting on, much like how I imagine most of the troops' daily rations will come from the areas they are marching through, just like it used to work in medieval times.
"Captured Fenrisians were enslaved and put to work providing materials for the Imperial armies. They were forced to lay makeshift roads across the treacherous glacial flats and made to cut down the huge trees of Fenris' forests to provide fuel for fires and the versatile engines of the Imperial Guard tanks. However, the Fenrisians were not easily tamed and they had to be guarded closely lest they try to rise against Bucharis and strike at his army where it would be most damaging. Whole communities were slaughtered and settlements razed to the ground. The hardy livestock of the few scattered farms were butchered for the troops to feast upon, the women were enslaved and the young and old were slaughtered and left for the large carrion crows that circle the skies of this inhospitable world."
-- 2E C:SoB, The Age of Apostasy
Needless to say, foraging and looting also makes the regiment much less dependent on a steady supply chain, which in many cases might be difficult to establish, given the unreliable nature of Warp travel. Prolonged campaigns would probably see the Munitorum establish a local chain of logistics, but this would take weeks if not months of organisation, not included the time it would take to first pacify the region where the required resources (including manpower) could be requisitioned.
I'm digressing, ain't I?
Back to lovemaking!
It is my interpretation and belief that any rules and habits concerning fraternisation would depend on an individual regiment's homeworld. You can have a regiment of men who only sleep with one another (hello, Spartans), just like you could have a regiment whose troops would be allowed to take slaves from the subjugated population of a recently conquered world (*cough*Columbus*cough*). And that's not even touching on mixed-gender regiments, where fraternisation might be allowed, discouraged or strictly forbidden all depending on local customs of the world that raised it. Go nuts! Almost anything goes - that's one of the greatest advantages of the Imperial Guard in terms of fluff.
As for the Cadians: according to the Codex EoT, every Cadian citizen is recruited into the Interior Guard, but only one in ten (chosen at random, to ensure an equal distribution of quality troops) is transferred into the Shock Troops and sent to fight off-world. Very much unlike your standard Guard regiment that either fights until destroyed or ends up being garrisoned somewhere, the Shock Troops also seem to rotate back into the Interior Guard after a tour of duty. This re-assimilation would allow it to "offload" children born during the campaign, bring valuable combat experience into units the surviving companies merge with, and be an option of retirement for old and/or crippled soldiers. As per the Codex, even though every single Cadian has at one point served in the Guard, only 71.75% of the population are actually under arms. This means that of a population of 250,000,000 people, about 70 million people are "free" to take care of civilian jobs or raise a family (including those too old to do anything, though).
Edited by Lynata, 28 August 2014 - 01:12 AM.