Child of parent position wrong

I'm trying to create a small square frame to appear next to my main player sprite, and then when the player moves the square moves with it. So I'm attaching the square as a child like this

Code (CSharp):

1. actionFrame.transform.parent = mainPlayer.transform

But it's not working. For some reason the position of the square is a negative version of the players current position, so if the player is at 500,500 then the square will be -500,-500

How can I make the square be at 0,0 and move with the player?

(I've tried setting the squares position after to 0,0 but it doesn't work).

 

The new position values represent the localPosition of the gameObject relative to the parent object.

If you're actionFrame is positioned at 0,0 and your parent at 500,500, the 'origin' of the object's local coordinates will no longer be the world coordinates 0,0 after parenting, but the parent's world coordinates.

So the world position 0,0 would now be -500,-500 in the vector space relative to the parent.
The local position 0,0 of your child transform will translate to 500,500 in world space

 

So I have to make my squares position the same as the target parent before making it a child of that parent? and then it's a child it's local/relative pos will be 0,0?

 

Or attach it and assign Vector2.zero (Vector3.zero respectively) to the childs transform.localPosition. That should work as well.