Get all child objects. (TestFile use OdinInspector)

GetAllChildren

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

public static class GetAllChildren_Object{
	public static GameObject[] GetAllChildren(this GameObject thisObj,bool getInvalid = false){
		return thisObj.GetComponentsInChildren<Transform>(getInvalid).Where(com => com != thisObj.transform).Select(com => com.gameObject).ToArray();
	}	
}
public static class GetAllChildren_Component{
	public static GameObject[] GetAllChildren(this Component thisCom,bool getInvalid = false){
		return thisCom.GetComponentsInChildren<Transform>(getInvalid).Where(com => com != thisCom.transform).Select(com => com.gameObject).ToArray();
	}
}

GetAllChildrenTest

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using Sirenix.OdinInspector;
using System.Linq;

public class GetAllChildrenTest : MonoBehaviour
{
	[Button]
	void GetAllChildren_Test(){
		GameObject[] children = gameObject.GetAllChildren();
		children.ToList().ForEach(x=>Debug.Log("Child:"+ x.name));
	}
}