Couldn't you just put a statue in the middle of the room and drop the babies on it? More compact than a ring of fortifications or windows. Also lets the audience have a closer view, and possibly enhanced splatter. Do fortifications stop flying body parts? I assume windows would.
Of course, there may be a difference of opinion on the splatter. Some people may prefer lots of it in the hope that being hit by flying baby/kitten/puppy parts will harden the dwarves up more quickly (but I doubt it would matter). But others might prefer to have the mess contained behind windows to avoid tracking blood all over the their nice, color coordinated floor patterns. Kind of the Ozzy Osborne vs. Martha Stewart debate.
I'm also wondering how one manages to get a baby dropped down a pit? They don't show up on the "pit an animal" menu, so I guess you'd have to get it on a retracting bridge and pull the lever. But how do you get it to go where you want? When I was doing !!SCIENCE!! on falling damage, I would assign Dwarven Test Subjects to a squad and tell the squad to move to the retracting bridge at the appropriate level of my 20z tall test chamber (you know, Dwarves are very trusting). But you can't do that with babies.
Well, you can put mom in a squad, but then you end up dropping her as well, which may not be what you want. I mean, sure it will help get the audience emotionally toughened up, but she might just have useful skills. On the other hand, this would be a good use for migrant potash makers. Drop them before they make any friends and they won't cause bad thoughts, but hey, a death witnessed is still a death witnessed. If you want to make heartless killing machines, you've got to break a few cheesemakers.
Oh, wait. If she's got a baby, she's probably already made at least one friend. But then, if we've progressed to dropping adults, we don't really need the baby any more (This is progress? Oy vey!)
One of these days, Toady will implement post-traumatic stress disorder and this all becomes worthless.
Keith