Magento - Data feed manager - add custom attribute

I am using data feed manager. Magento 1.9.4.x

I have custom pattern and it is working. You can see below. I would like to add 'barcode' attribute to my pattern.

- I want to show barcode value of child product.
- Inside of below code.

<?
$childProducts = Mage::getModel('catalog/product_type_configurable')
->getUsedProducts(null,$product);
$stock_count=0;
$sizeqty="";
foreach($childProducts as $child){
if($child->getAttributeText('ayak_no')!=""){
$sizeqty.="<Stok><isim>Numara</isim><Beden>".$child->getAttributeText('ayak_no')."</Beden><Miktar>".(int)Mage::getModel('cataloginventory/stock_item')->loadByProduct($child)->getQty()."</Miktar></Stok>";
}
if($child->getAttributeText('ust_beden_no')!=""){
$sizeqty.="<Stok><isim>Beden</isim><Beden>".$child->getAttributeText('ust_beden_no')."</Beden><Miktar>".(int)Mage::getModel('cataloginventory/stock_item')->loadByProduct($child)->getQty()."</Miktar></Stok>";
}
}
return $sizeqty;
?>