def get_only_child(node):
    """
    Returns the only child of a node which has only one child. Returns 'None' if node has 0 or >1 children
    """
    child_count = 0
    only_child = None
    for key in node:
        if isinstance(key, int):
            child_count += 1
            only_child = node[key]
    return only_child if child_count == 1 else None