A Proper ExclusiveChildren script for Unity Editor

ExclusiveChildren.cs

using UnityEngine;
using System.Collections;
#if UNITY_EDITOR
using UnityEditor;
#endif

//See http://g.recordit.co/sYme8QQg2L.gif for an example of usage
public class ExclusiveChildren : MonoBehaviour {

#if UNITY_EDITOR
	void OnDrawGizmos() {
		if (EditorApplication.isPlaying)
			return;
		if (Selection.activeGameObject == null)
			return;
		if (Selection.activeGameObject == gameObject)
			return;
		if (! Selection.activeGameObject.transform.IsChildOf (transform))
			return;

		DeactivateAllChildrenNotParentOf (Selection.activeGameObject.transform);
	}

	void DeactivateAllChildrenNotParentOf(Transform transform) {

		int childCount = this.transform.childCount;

		for(int i = 0; i < childCount; i ++) {
			Transform childTransform = this.transform.GetChild (i);
			childTransform.gameObject.SetActive (transform.IsChildOf(childTransform));
		}
	}
#endif
}