El cheapo way to fix the nested stopcoroutine problem

Foo.cs

class Foo : MonoBehaviour 
{
    Coroutine m_coroutine;
    readonly HashSet<IEnumerator> m_innerCoroutines = new HashSet<IEnumerator>();

    public void StartThing()
    {
        m_coroutine = StartCoroutine(ParentCoroutine());
    }
    
    public void EndThing()
    {
        if (m_coroutine != null)
        {
            StopCoroutine(m_coroutine);
            m_coroutine = null;
            
            foreach (var innerCoroutine in m_innerCoroutines)
                StopCoroutine(innerCoroutine);
            m_innerCoroutines.Clear();            
        }
    }
    
    public IEnumerator ParentCoroutine()
    {
        yield return StartAndTrack(ChildCoroutine(1));
        yield return StartAndTrack(ChildCoroutine(2));
        yield return StartAndTrack(ChildCoroutine(3));
    }
    
    IEnumerator StartAndTrack(IEnumerator _coroutine)
    {
        m_innerCoroutines.Add(_coroutine);
        yield return _coroutine;
        m_innerCoroutines.Remove(_coroutine);
    }    
    
    public IEnumerator ChildCoroutine(float _varyingInput)
    {
        // do stuff based on input
    }
}