So how do you manage to seperate the children out in the first place? I wonder if you could force them into cages, that would be good, it even improves FPS a bit.
For my Dwarven Children's Academy, I used a system of pressure plates set to trigger for citizens in a size range chosen so only dwarven children would trigger it. The child diverters were placed in high-traffic corridors in the main fortress, so that children would inevitably step on them eventually. Stepping on the pressure plate would open floor hatches before and after, which would trap the child in place, and open up a side door leading to a passage to the academy. The child would have no choice but to proceed down the side passage. In the academy I had a similar mechanism set to trigger for adults, so when a child grew up he would be automatically sent back to the main fortress.
The Academy had a craftdwarf's workshop for strange moods, and I had a system set up so I could drop materials in from above. The idea was that if a child went into a mood, I could look at his demands and then choose exactly what kind of metal or rock or whatever I wanted his artifact to be made from. The children didn't do any other useful work, but just spent all their time hanging out under a waterfall becoming super happy from the mist and gaining legendary social skills. In retrospect it would have been clever to put vital fortress defense levers under there, since children will pull levers and would never have been far from them, but I built the fortress defenses long before I thought of making the academy.