aui-form-builder-field-checkbox.js

renderUI: function() {
  var instance = this,
      templateNode = instance.get('templateNode'),
      labelNode = instance.get('labelNode');

  A.FormBuilderCheckBoxField.superclass.renderUI.apply(instance, arguments);
  
  // labelNode.insert(templateNode, labelNode, 'before');
  
  // Works, result is <input><label></label></input>
  templateNode.prepend(labelNode);
  
  // Does not work, result is just <label></label>
  labelNode.prepend(templateNode);
}

aui-form-builder-field.js

_uiSetLabel: function(val) {
  var instance = this,
      labelNode = instance.get('labelNode');

  // This line right hereee
  labelNode.setContent(AEscape.html(val));
}