Question How to update dynamically the UI button used with ''On Select''?

Hi,

I have a script with an empty variable ''Child2''. On Start, I assign a game object to the variable ''Child2''.
The assigned game object is a UI button.

The script defines some actions when the button contained in the variable ''Child2'' is selected (On select event).
But even though I assigned On Start the button to ''Child2'', the On Select Event keeps considering ''Child2'' as empty.
If I use the debug, it confirms that ''Child2'' was updated, but not with On Select Event. Please see the screenshot.

1- Is this the expected behaviour?
2- If yes, why was it designed that way?
3- How can I change the content of Child2 and have On Select event take it into account? The reason I need this is that I want to use the same script for many different objects and I don't want to hardcode the value of Child2, Instead, Child2 will contain the child with the index2 of the game object the script is assign to.

Thanks!