Boolean Condition On Child Button

Hi, so I have adding Child button. I can make it works while making the button manually. But Im confused on how this works since It only have 1 Event button.
What I want :

  1. Click button 0 (Active), after that click button 1 (Active), button 0 (Disable)
  2. When I click again button 1 it will (Disable).

I got it works, but when there is a button that still green, when click other button it makes the button red instead of green. How to make boolean keep true instead of false when click other buttons ?