{% for subfield in field %}
    <div class="i-radio">
        {{ subfield() }}
        {{ subfield.label }}
    </div>
{% endfor %}

{% for subfield in field %}
    <div class="i-radio">
        {{ subfield(required=field.flags.required) }}
        {{ subfield.label }}
    </div>
{% endfor %}

Add required on radio buttons wtforms widget
Add required on radio buttons wtforms widget
