I have a player object with a NetworkIdentity commponent and 1. child object.
Thats my simple code which will run with a key press.

    [Command]
    void CmdTellServerToTellClientToChangePosBack(Transform trans) {
        RpcTellClientToMoveContainerBack(trans);
    }
    [ClientRpc]
    void RpcTellClientToMoveContainerBack(Transform tran) {
        if (tran == null) return;
        tran.position = Vector3.zero;
    }

Then I get this LogWarning Attempted to sync a Transform (Item Slot 1 (UnityEngine.Transform)) which isn't networked. Transforms without a NetworkIdentity component can't be synced. Why?

I tryed to moven an object and sync it to the other clients which end evertime with this logWarning.