Unity2DComponents.cs

using System.Linq;
using UnityEditor;
using UnityEngine;

public static class Unity2DComponents
{

    [MenuItem("GameObject/2D Object/Box", false, 0)]
    private static void Create2DCube()
    {

        var gameObject = GameObject.CreatePrimitive(PrimitiveType.Cube);

        if (Selection.activeGameObject)
        {

            gameObject.transform.parent = Selection.activeGameObject.transform;

        }

        gameObject.name = GenerateNameForGameObjectWithComponent<BoxCollider2D>(gameObject, "Box");

        Object.DestroyImmediate(gameObject.GetComponent<BoxCollider>());

        gameObject.AddComponent<BoxCollider2D>();

        Selection.activeGameObject = gameObject;

    }

    [MenuItem("GameObject/2D Object/Circle", false, 0)]
    private static void Create2Sphere()
    {

        var gameObject = GameObject.CreatePrimitive(PrimitiveType.Sphere);

        if (Selection.activeGameObject)
        {

            gameObject.transform.parent = Selection.activeGameObject.transform;

        }

        gameObject.name = GenerateNameForGameObjectWithComponent<CircleCollider2D>(gameObject, "Circle");

        Object.DestroyImmediate(gameObject.GetComponent<SphereCollider>());

        gameObject.AddComponent<CircleCollider2D>();

        Selection.activeGameObject = gameObject;

    }

    private static string GenerateNameForGameObjectWithComponent<T>(GameObject gameObject, string name) where T : Component
    {

        T[] others;

        if (gameObject.transform.parent)
        {

            others = gameObject.transform.parent.GetComponentsInChildren<T>()
                .Where(t => t.transform.parent.Equals(gameObject.transform.parent)).ToArray();

        }
        else
        {

            others = Object.FindObjectsOfType<T>()
                .Where(t => t.transform.parent == null).ToArray();

        }

        var updatedName = name;

        if (others.Length > 0)
        {

            updatedName = string.Format("{0} ({1})", updatedName, others.Length);

        }

        return updatedName;

    }

}