Button as a child of a button

I've been using Unity in about five months now, and I've been working on a project for last few weeks, and it's almost finished. And I want to implement shop UI for my project. And when I attached a button as a child of my shop UI and add a listener to it from a script. it did work. But when I clicked on a parent button the child button is also clicked. So I want my parent button just to change a color for my model as preview, and the child button to buy/set the color if already owned. So the question is. Is there something wrong with my design or it was my script? or I just can't have a button as a child of another button? Thanks before, any help would be appreciated.

Here is my code to add a on click listeners

 void SetShopButtons()
     {
         int i = 0;
 
         foreach (Transform t in colorViewport)
         {
             int currentIndex = i;
             Button b1 = t.GetComponent<Button>();
             Button b2 = b1.GetComponentInChildren<Button>();
             Text buySetText = b2.GetComponentInChildren<Text>();
 
             b1.onClick.AddListener(() => OnColorSelect(currentIndex, buySetText));
             b2.onClick.AddListener(() => OnColorBuySet());
 
             if (SaveManager.Instance.OwnedColorCheck(i))
                 buySetText.text = "Owned";
             else if (i == activeColorIndex)
                 buySetText.text = "Current";
             else
                 buySetText.text = colorPrice[i].ToString();
 
             i++;
         }
     }