/**
 * @var BlockFactory
 */
protected $blockWrapperFactory;

/**
 * Constructor
 *
 * @param TemplateContext $context
 * @param UiComponentInterface $component
 * @param BlockFactory $blockWrapperFactory
 * @param array $data
 */
public function __construct(
    TemplateContext $context,
    UiComponentInterface $component,
    BlockFactory $blockWrapperFactory,
    array $data = []
) {
    $this->component = $component;
    $this->blockWrapperFactory = $blockWrapperFactory;
    $this->setNameInLayout($this->component->getName());
    parent::__construct($context, $data);
}

/**
 * Render block HTML
 *
 * @return string
 */
protected function _toHtml()
{
    foreach ($this->getChildNames() as $childName) {
        $childBlock = $this->getLayout()->getBlock($childName);
        if ($childBlock) {
            $wrapper = $this->blockWrapperFactory->create([
                'block' => $childBlock,
                'data' => [
                    'name' => 'block_' . $childName
                ]
            ]);
            $this->component->addComponent('block_' . $childName, $wrapper);
        }
    }

    $result = $this->component->render();
    return (string)$result;
}