class Cart extends MagentoFrameworkAppActionAction
{
    protected $_cart;
    protected $productRepository;
    protected $formKeyValidator;

    public function __construct(
        MagentoFrameworkAppActionContext $context,
        MagentoCheckoutModelCart $cart,
        MagentoCatalogApiProductRepositoryInterface $productRepository,
        MagentoFrameworkDataFormFormKeyValidator $formKeyValidator
    ) {

        $this->_cart = $cart;
        $this->productRepository = $productRepository;
        $this->_formKeyValidator = $formKeyValidator;

        return parent::__construct($context);
    }

    public function execute()
    {
        if (!$this->_formKeyValidator->validate($this->getRequest())) {
            return $this->resultRedirectFactory->create()->setPath('*/*/');
        }

        $qtys       = $this->getRequest()->getParam('qty');
        $childIds   = $this->getRequest()->getParam('child_ids');

        $productstoadd = array();
        foreach ($qtys as $parentId => $array) {
            if (is_array($array)) { //configurable products
                foreach ($array as $attributeId => $child) {
                    foreach ($child as $childId => $value) {
                        if ($value != 0) {
                            $productstoadd[$parentId][$attributeId][$childId] = $value;
                        }
                    }
                }
            } else {
                // simple products

            }
        }

        foreach ($productstoadd as $productId => $data) {
            foreach ($data as $attributeId => $child) {
            foreach ($child as $childId => $qty) {
               //reload product
                $_product = $this->productFactory->create()->setStoreId($storeId)->load($productId);
                $options = array(
                    $attributeId => $childId,
                );

                $params = array(
                    'form_key' => $this->getRequest()->getParam('form_key'),
                    'product' => $productId,
                    'super_attribute' => $options,
                    'qty' => $qty,
                    'selected_configurable_option' => $childIds[$productId][$attributeId][$childId],
                );

                $this->_cart->addProduct($_product, $params);
            }
        }        }
        $this->_cart->save();
        return $this->resultRedirectFactory->create()->setPath('checkout/cart');
    }
}