{% load thumbnail %}

<div class="row">
    {% for child in category.get_children %}
        <div class="col-xs-6 col-sm-6 col-md-4 col-lg-4">
            {% thumbnail child.image "x150" upscale=False as thumb %}
            <a href="{{ child.get_absolute_url }}" class="text-center">
                <img style="height:100%;" src="{{ thumb.url }}" alt="{{ child.name }}" class="thumbnail img-responsive center-block">
                <h6>{{child.name}}</h6>                    
            </a>
            {% endthumbnail %}
        </div>
    {% endfor %}
</div>