{% for item in items %}
    {% if forloop.parentloop %}
        {% with forloop.parentloop.counter as parent_counter %}
            {% with forloop.counter as child_counter %}
                {% ifequal parent_counter 1 %}
                    {% cycle 'A', 'B', 'C' as letter silent %}
                {% else %}
                    {% cycle 'D', 'E', 'F' as letter silent %}
                {% endifequal %}
                {{ letter }}{{ child_counter }}
            {% endwith %}
        {% endwith %}
    {% else %}
        {% cycle 'A', 'B', 'C' as letter silent %}
        {{ letter }}{{ forloop.counter }}
    {% endif %}
{% endfor %}