find next gameobject in hierarchy?

hey, how can i find find a GameObject that is under the current GameObject?
so if the hierarchy is like this
-root
–obj1
–obj2
–obj3

i wanna do something like:

public class Findnext : MonoBehaviour {

	public GameObject next;
	

	// Use this for initialization
	void Start () {

		//if this script is on obj1 - next = obj2
        //if this script is on obj2 - next = obj3
	
	}

81969-chil.png
81970-deb.png

using UnityEngine;
using System.Collections;

public class WhereIsThis : MonoBehaviour
{
	// Use this for initialization
	void Start ()
	{
		Transform nextChild = this.NextChild ();

		if ( nextChild == null )
			Debug.LogFormat ("{0} is the last sequential child or didn't have a parent!", this.name);
		else
			Debug.LogFormat ("{0} has a next sequential child named {1}!", this.name, nextChild.name);
	}
	
	// Update is called once per frame
	private Transform NextChild ()
	{
		// Check where we are
		int thisIndex = this.transform.GetSiblingIndex ();

		// We have a few cases to rule out
		if ( this.transform.parent == null )
			return null;
		if ( this.transform.parent.childCount <= thisIndex + 1 )
			return null;

		// Then return whatever was next, now that we're sure it's there
		return this.transform.parent.GetChild (thisIndex + 1);
	}
}