Get "world" position of grid children

From a C# script, how can I get the actual world position of the children of a grid (grid as in a Canvas with a Grid Layout Group added)? The position would be relative to some super parent that I will specify, not the position in the grid itself.

In my case I have a Canvas-grid with 25 Image children, neatly spaced out. The Canvas-grid in turn is a child of a bigger Panel. So I would like to know the position of each Image relative to the outer Panel.

What I have tried:

Iterating through all children of the grid.transform. The child.position and child.localPosition is the same for all the children - it appears that value is not in use because visibly the children are NOT at the same position.

Set the outer panel position to 0,0,0 then on each image use transform.localPosition