One thing that personally comes naturally to mind with the recent discussion of outlying community sprawl here is the idea of court life.
The Barron, Count, Duke and King should realistically receive representatives from outlying communities in their domain delivering them information, local requests and offered goods and dispatching them back with instructions and agreements. As well they'd periodically be traveling around their own domain and going to the court of the local noble next up the chain of command and similarly receiving those from the next level down the chain.
Of course to really handle this properly, once your fortress has a Mayor (ie you're big enough for someone higher up to care you exist at all) you should occasionally have mandates and demands delivered from these nonlocal officials as well as appropriate means to make requests from them. Aside from this you should have appropriate rooms for the next level individual because they'll occasionally come visit. Giving them unhappy thoughts should make them less likely to comply with your requests as well. Once the higher nobles come to live in your fortress they should need extra bedrooms, etc. of appropriate quality and enough room in their office/throne room for their visiting lesser noble guests as well.
Aside from this you really shouldn't see large migrant waves beyond this size without requesting additional manpower (a few small ones here and there is a different matter though) and the caravans probably shouldn't bring much unless you request it at this point.
I'm bringing all this up though because it's unclear to me from either the former or current dev pages whether Toady has given as much consideration to realistic civilian bureaucracy as he has on the military side. The closest I can remember seeing are having your local militia called up as part of a larger army and improved diplomacy.
I of course realize this is all really dependent on stuff that is still unimplemented like dwarves being able to leave the local map.
Or they could have other reasons for taking the children of other civilizations.
That movie was iirc one of toadys inspirations for the snatching thing.
IT would be cool thought if the gobins would have a preverence for catchyMusic and musicals as only form of art they know.
Of course the snatching thing is part of the traditional mythos of the Fae, of which Elves, Dwarves, Goblins and other standard fantasy races were all part (changlings being the most common).