Hi,
I just tested with a cube and cube child, both with rigidbody and it works and i have corrected the warning errors (has no impact on gameplay - thanks for info). What you trying to do is a bit different than the purpose of the action. The action will set parent and (if true) all child. You don't need a collider (no impact) if you select only rigidbody from drop-down so I don't understand why/how collider is affecting the rigidbody (I also tested and no issue). I believe you have the wrong setup or you the action is not what you need.. Detect collision is turned off - maybe delete line 246 and tests to see is that helps(?)