FixSize.cs

using UnityEngine;
using System.Collections;

public class FixSize : MonoBehaviour
{
    private float currentSize = 0.5f;
    public Transform[] objects;
    void Update ()
    {
        for(int i = 0; i<objects.Length; i++)
        {
            objects[i].localScale = new Vector3(currentSize,currentSize,currentSize);
        }
    }
    void OnGUI()
    {
        currentSize = GUI.HorizontalSlider(new Rect(Screen.width-350, Screen.height-60, 300, 30), currentSize, 0.0F, 2.0F);
    }
}