MonoBehaviour.OnTransformChildrenChanged()

Description

Called when the list of direct children of a GameObject's Transform changes.

The following changes to direct children of a GameObject invoke OnTransformChildrenChanged:

• Adding a new child object to the GameObject's Transform.
• Removing a child object.
• Moving a child to a different parent.
• Changing the order of the direct children.

It makes no difference whether these actions are performed in the Hierarchy window or from code with APIs such as Transform.SetParent, Object.Destroy, or Transform.SetSiblingIndex.

OnTransformChildrenChanged is only triggered by changes to the immediate (direct) children of the Transform. Changes to grandchildren or deeper descendants do not invoke this method on the parent.

OnTransformChildrenChanged is called at runtime when a GameObject's direct children change. It can also be called in Edit mode if scripts use ExecuteInEditMode or ExecuteAlways.

Use this callback to respond to changes in your GameObject's immediate child hierarchy, such as updating UI elements, managing child object lists, or refreshing cached references.

Additional resources: MonoBehaviour.OnTransformParentChanged.

// Attach this script to any GameObject (for example, an empty "Parent" object).
// Assign a UI Text component to the countText field in the Inspector.
// Add or remove children from the GameObject at runtime or in the Editor.

using UnityEngine;
using UnityEngine.UI;

public class ChildrenCounter : MonoBehaviour
{
    public Text countText;

    private void Start()
    {
        UpdateChildrenCount();
    }

    // Called by Unity when a child is added or removed
    private void OnTransformChildrenChanged()
    {
        UpdateChildrenCount();
    }

    private void UpdateChildrenCount()
    {
        int childrenCount = transform.childCount;
        if (countText != null)
        {
            countText.text = $"Children: {childrenCount}";
        }
    }
}