To get all the children product ids from the configurable product in Magento 2, you need to retrieve the list of child item ids by the configurable product id.

<?php
namespace MagemonkeysChildIdsModel;

use MagentoConfigurableProductModelProductTypeConfigurable;

class ConfigurableChildrenIds
{    
    private $configurable;
    public function __construct(
        Configurable $configurable
    ) {
        $this->configurable = $configurable;
    }
    
    public function getChildrenIds(int $id)
    {
        $childItemId = $this->configurable->getChildrenIds($id);
        return $childItemId;
    }
} ?>

List out the children items id for a configurable product by using below commands.

$configurableId = 1478;
$superAttributeByChild = $this->getChildrenIds($configurableId);