The problem with the giant creatures is that punching and kicking them has no effect and that's all your dwarves do if they are not in a squad, however these giant creatures also usually get beaten unconscious quickly because all of your dwarves are usually hitting them in the head which means it will kill more dwarves by canceling their drinking and eating then by killing them itself. However after I had this problem a few times I found that if you just assign some dwarves to a squad with metal weapons or even just wooden weapons they will find some sort of tool and use that instead of just punching the thing.
Thank you! I had one fort where a crocodile ambushed one of my seven almost immediately on embark. Four others ran over to help him -- but once the croc let go, rather than carry their semiconscious comrade to safety, they insisted on continuing to kick and punch the semiconscious crocodile while their companion bled out, until they all nearly died of thirst.
If you have a burrow a long way from the conflict, you can set it as an alert zone thingy and all the civilians run there and stop attacking. Downside is the job cancellations.