Here, you can use VisualTreeHelper:
for (int i = 0; i < VisualTreeHelper.GetChildrenCount(contentControl); i++)
{
var child = VisualTreeHelper.GetChild(contentControl, i);
if(child is ContentPresenter)
{
var contentPresenter = child as ContentPresenter;
for (int j = 0; j < VisualTreeHelper.GetChildrenCount(contentPresenter); j++)
{
var innerChild = VisualTreeHelper.GetChild(contentPresenter, j);
}
break;
}
}