Get children using a tag

Why does unity not have this function yet?

Code (CSharp):

1. GameObject GetChildWithTag(GameObject Obj, string tag)
2.     {
3.         for(int i = 0; i < Obj.transform.childCount; i++)
4.         {
5.             if(Obj.transform.GetChild(i).tag.CompareTo(tag) == 0)
6.             {
7.                 return Obj.transform.GetChild(i).gameObject;
8.             }
9.         }
10.         return null;
11.     }
12.     List<GameObject> GetChildsWithTag(GameObject Obj, string tag)
13.     {
14.         List<GameObject> Children = new List<GameObject>();
15.  
16.         for (int i = 0; i < Obj.transform.childCount; i++)
17.         {
18.             if (Obj.transform.GetChild(i).tag.CompareTo(tag) == 0)
19.             {
20.                 Children.Add(Obj.transform.GetChild(i).gameObject);
21.             }
22.         }
23.         return Children;
24.     }

Is it too expensive?