Right now, I'm working on a short film about a knight and i'm trying to attach a sword to the knight's hand. I tried to attach the sword asset to the hand, but whenever I do, it's like the sword becomes the root of the object the entire arm. It's hard to explain, so i'll let screenshots tell the story.
Check the section on "Gizmo handle position toggles" here: https://docs.unity3d.com/Manual/PositioningGameObjects.html I think you'll want to click the one that says "Center" so that it says "Pivot".