Getting 'Object Reference not set' when calling function from instantiated object

I have a game where the user drags ‘Trampolines’ into a scene, then fires a cannon, the cannonball bounces off the trampolines and eventually through a hoop. As there can be more than one trampoline I’m instantiating them at the start.

The GameManager decides how many trampolines should be spawned and adds each one to a list. When the cannon is fired it makes a call to the trampoline script to deactivate the rotation arrows around the trampoline. But no matter what I do, this call gives the ‘Object Reference not set to an instance of an object error’.

The GameManager code -

 public Trampoline trampoline; 
 public int trampolineCount;
 public List<GameObject> trampolineList = new List<GameObject>();

void Start()
        for (int i = 0; i < trampolineCount; i++)

    public void CannonFired()
        foreach (GameObject go in trampolineList)
         //TrampolineStandard is the name of the script on the trampoline
        TrampolineStandard trampScript = go.GetComponent<TrampolineStandard>();

The Trampoline code

    public GameObject arrowLeft;
    public GameObject arrowRight;

    public void HideArrows()

I assume this bug is coming from the object being instantiated, but how the fudge do I fix it

For anyone interested I fixed it. The trampoline script was attached to a child of the trampoline prefab.
This line of code was the answer -

TrampolineStandard trampScript = go.GetComponentInChildren(TrampolineStandard)();