get ugui prefab's child

I have an ugui prefab instantiate by code and want to get its child as reference.
My prefab is grouped as:
myCanvas
--Image1
--Image2
--Text1
I try to get it by findchild but getting the error
Cannot convert type UnityEngine.Transform' to UnityEngine.UI.Image'

 Image speechUIImage;
 Text speechUiText;
 void Start () {
         GameObject speechUI = Resources.Load ("SpeechUI/SpeechUIObject") as GameObject;
 
         Instantiate (speechUI);
 
         speechUIImage = speechUI.transform.FindChild ("Image");
 }