AddChild

using UnityEngine;

using UnityEngine;

using UnityEditor;

using System.Collections;

public class AddChild : ScriptableObject

{
[MenuItem ("GameObject/+Add Child")]

    static void MenuAddChild()

    {

        Transform[] transforms = Selection.GetTransforms(SelectionMode.TopLevel | SelectionMode.OnlyUserModifiable);
foreach(Transform transform in transforms)

        {

            GameObject newChild = new GameObject("_null");

            newChild.transform.parent = transform;

        newChild.transform.localPosition = Vector3.zero;

        }
}
}

AddChild