I wish I had taken screenshots of this all happening because it was pretty brutal. The fort has advanced some months since and I wasn't planning on posting about it, but here's what was going on...
While busy setting up stockpiles below surface, I notice some combat reports are active. Initially, upon seeing the blood-filled tunnel, the undead boar corpses, and a combat log of a werebear baby that had just mauled them all to death... I thought one of my child migrants was a werebaby! Such excitement. For context, I am in a reanimating biome, 3 migrant waves in, and 90% of wildlife that roams about is undead. Thus far I've received 3 children and a bunch of pretty interesting dwarves that aren't totally useless.
I decide to construct rooms to lock up the children migrants of my current fort to discover the identity of the werebear baby. Combat report states the name Kammat Laslemedi, and no child of ours is named that. Then I noticed an announcement about the arrival about Kammat Laslemedi caught in 1 of the 2 cage traps in an underground escape tunnel leading to my fortress. The other cage trap had captured a undead boar sow at the time, part of the pack. I can see now he is a human child, but no idea how old he is.
The vengeance is sweet, because this pack of boars had actually brutally murdered two of my starting seven, a Mechanic, and a Miner/Grower. However, now that I have the captured human werebear baby (or rather, he captured himself), he has matured into an adult. I think of building a tower perhaps, equipping him with a weapon and shield, and unleashing him when needed. As a werebaby, he dealt with the boars unlike my two starting hammerdwarves could ever have dreamed of. As a werebear adult, equipped with weapons, I don't know. Maybe he will be unable to wield weapons because he's a bear, time will tell.