[Unity3D] Editor script that counts object count of all children of selected prefab/game object

ObjectDeepCount.cs

using System.Linq;

using UnityEditor;

using UnityEngine;

public class ObjectDeepCount : MonoBehaviour {

    [MenuItem("Assets/Count objects")]
    private static void DeepCountObjectHierarchy() {
        foreach (GameObject o in Selection.objects.OfType<GameObject>()) {
            Debug.Log(string.Format("Children count: {0}", CountChildren(o.transform)));
        }
    }

    public static int CountChildren(Transform go) {
        int count = 0;

        foreach (Transform child in go.transform) {
            count += CountChildren(child); // add the number of children the child has to total
            ++count; // add the child itself to total
        }

        return count;
    }

}