I think there is a low % chance of a trap triggering for any kobold type creature so a long trap hall may catch them as the odds for the series add up putting the animal closer to the center of a trap line will uncover them in the midst of the traps -- no escape
Maybe I'm just not trapping my entrance enough then!
But I don't really think that them being sneaking or not has anything to do with triggering the traps. I've seen plenty of kobolds appear after having slipped my line of traps and happily walk right back out (goblins trigger first one on the way in while sneaking).
Also,
http://df.magmawiki.com/index.php/KoboldThey can go through locked doors and they are not affected by traps.
However I've seen a couple of them caught in cage traps. But those are most likely because any creature that falls unconscious on top of a trap (even with the [TRAPAVOID] tag) will trigger it. And they were fighting the local militia on top of the traps at the time (caught one of the dwarves as well who died on the way to the animal stockpile).
Maybe that animal you have in the midst of all the traps is mauling them badly, causing them to trigger the traps?
In that case I need to know what you're using, since anything I put there mostly gets stabbed as the kobold turns tail and run.