I know that every moving collider object should have also a rigidbody. Is this rule valid for colliders parented by a rigidbody ? Or do they become somehow dynamic colliders ?
What if I need additional colliders as child objects under the rigidbody? Say, they are not kinematic, they don’t even have a rigidbody. Only the parent is rigidbody.
Does the parent rigidbody make the children colliders dynamic or are they still static ?(which is weird, the static colliders parented by a moving rigidbody, loosing too much performance)
No, it’s not. The the rigidbody aggregates all of the colliders under it at runtime. Plus, colliders with rigidbodies aren’t considered static colliders, and the table doesn’t include them for the reason of having to recalculate the entire collision matrix every time one is moved, as you noted.
It is safe to have several colliders childed to a single rigidbody, and to only move objects with colliders that also have rigidbodies attached.