Answer by Paparakas

Ok so I actually know this one since I've had some frustrating moments with it in my own project. If the parent is a rigidbody and the children are all exclusively colliders, it will act as a compound collider. You can look that up in the documentation. It basically just means a rigidbody comprised of multiple colliders. Either way, if you were to cast a ray to any of the colliders within the compound collider, RayCastHit hit would give you the parent (the one with the rigidbody). If you want to get the individual colliders you'd do hit.collider. I hope this helps at least somewhat.