File Classes.cs
----------------------------------------
using UnityEngine;
using System;

[Serializable]
public class BaseClass
{
    public float SomeValue;

    public virtual void SendMessage()
    {
        Debug.Log("There's nothing here!");
    }
}

[Serializable]
public class ChildClass : BaseClass
{
    public string SpecialMessage;

    public override void SendMessage()
    {
        Debug.Log("Message for you Sir! " + SpecialMessage);
    }
}
----------------------------------------
File: Beda.cs

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

public class Beda : MonoBehaviour
{

    public List<BaseClass> myValues = new List<BaseClass>();


    public void Start()
    {
        for(int i = 0; i< myValues.Count; i++)
        {
            Debug.Log(myValues[i].GetType().Name);
        }
    }
}

#if UNITY_EDITOR
[CustomEditor(typeof(Beda))]
public class BedaEditor: Editor
{
    public override void OnInspectorGUI()
    {
        base.OnInspectorGUI();

        if(GUILayout.Button("Create 2 BaseClass and 2 ChildClass"))
        {
            var bedaScript = (Beda)target;

            bedaScript.myValues.Clear();

            bedaScript.myValues.Add(new BaseClass());
            bedaScript.myValues.Add(new BaseClass());
            bedaScript.myValues.Add(new ChildClass());
            bedaScript.myValues.Add(new ChildClass());

            for(int i = 0; i < 4; i++)
            {
                Debug.Log($"Item #{i} Type {bedaScript.myValues[i].GetType().Name}");
            }
        }
    }
}

#endif