Use this in Unity to quickly give the children of a transform a number. You can use a prefix to replace their existing name, a suffix to add information after the number, and choose to start from zero.

NumberiseChildrenUtility.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

[ExecuteInEditMode()]
public class NumberiseChildrenUtility : MonoBehaviour
{
    //Use https://gist.github.com/adamski11/bd61693a1f90130c536d080496012ed9 to use a button in the inspector
    //[TestButton("Numberise Children", "NumberiseChildren")]
    [Header("Click to Run")]
    public bool shouldRun = false;

    [Header("Values")]
    public string prefix = "";
    public string suffix = "";
    public int countBackIndex = 0;
    public bool startAtZero = false;
    public bool includeSpaceBeforeNumber = true;

    void Update()
    {
        if(shouldRun)
        {
            NumberiseChildren();
            shouldRun = false;
        }
    }

    void NumberiseChildren()
    {
        for (int i = 0; i < transform.childCount; i++)
        {
            string newName = transform.GetChild(i).name;

            if (prefix != "")
                newName = prefix;

            newName = newName.Substring(0, newName.Length - countBackIndex);
            newName = newName + (includeSpaceBeforeNumber ? " " : "") + (startAtZero ? i : i+1) + suffix;
            transform.GetChild(i).name = newName;
        }
    }
}