I used to have to regularly clear the kids out of the troll cages by way of dumping them onto an artifact hatch in an engraved statue garden, by way of a 35 z tower extending entirely up out of the fort.
They joined the regular crundle and rutherer purges in horrifying my dorfs until I accidentally created a bloodcano by forgetting I originally designed the system so I could open the hatch and drop stuff onto the open space under a bridge controlled by a second lever, and a year or so in game later forgot why I did this, deciding to rebuild the bridge while redesigning stuff, and choosing to link it to the hatch lever.
After a good 30+ deaths ontop of it one day I ordered the lever pulled and my decision to ALSO have the drop shaft work as a mist generator due to a waterfall I can turn on and off meant there were fortifications around it in all of the bedroom and workshop areas above the gore-hatch... so the hatch opens, the giblets drop onto the drawbridge, which opens a second later, producing an unbelievable explosion of body parts and blood erupting upwards through a good five z levels of my fortress.
Where was I going with this... oh yeah, trolls happily bred just fine in cages, now would probably have to put them in a breeding facility or maybe a single cage to get them to keep breeding.