Unity3D Object is null after initialization in Start()

Question

I am trying to make a few objects and classes interact. I have two classes. Code is similar. But in class Building_main after object is initialized in Start() I can reuse it in functions and in class House_main I can not (object is null). class Building_main is a child of class House_main .

What am I doing wrong?

First class :

    public class Building_main : MonoBehaviour {

        public string owner;
        public string producedGoodName;

        private Building_goods goods;
        private House_main house;

        void Start () {
            goods = this.transform.Find("Building_goods").GetComponent<Building_goods>();
            house = this.transform.parent.gameObject.GetComponent<House_main> ();
            UpdateHouseInfo ();
        }

        void UpdateHouseInfo () {
            // reusing objs (house, goods) no error
            house.UpdateGoodInfo (goods.GetGoodByName("sword"), "sword");
        }

Second class :

public class House_main : MonoBehaviour {

    public string owner;

    private House_goods goods;

    void Start () {
        // obj (goods) is not null
        goods = this.transform.Find("House_goods").GetComponent<House_goods>();
       // i can use
       // goods.AddAmountToGoodByName (value, name);
    }

    public void UpdateGoodInfo (int value, string name) {
        // obj (goods) is null
        goods.AddAmountToGoodByName (value, name);
    }
}

Answer 1

Looks like my child class ( class Building_main ) Start() function is executing before parent class ( class House_main ) Start() function.

So in class House_main object goods is not yet assigned when I am calling function UpdateGoodInfo , because I am calling it using class Building_main Start()

`class Building_main {
        Start() {
          UpdateHouseInfo ();
        }
}`

Didn't know this.