Access Inner Blocks on the Parent Block during the PHP Block Render : https://jeffreycarandang.com/how-to-access-innerblocks-attributes-within-the-parent-block-on-the-wordpress-gutenberg-editor/

render.php

<?php
/**
 * Render Custom Block
 *
 * @param  array    $atts    Block Attributes
 * @param  string   $content Block Content (InnerBlocks)
 * @param WP_Block $block_class Block Class Instance
 * @return string          Block Markup
 */
function render( $atts, $content, $block_class ) {

	// Check how many inner blocks are available
	$item_count = $block_class->inner_blocks->count();

	if ( $item_count < 1 ) {
		return '';
	}
	
	ob_start();
	?>
	<div>
		<?php
			// iterate over the available inner blocks
			for ( $index = 1; $index <= $item_count; $index++ ) :

				// Get the inner block data
				$inner_block = $block_class->inner_blocks->current(); 
				
				// Holds the inner block attribute
				$attribute   = $inner_block->attributes;

				// This will display the attributes data
				var_dump( $attribute );

				// increase the index in the WP_Block_List class used to retrieve the current block
				$block_class->inner_blocks->next();
			endfor;
				// reset the index in the WP_Block_List class to the initial state
				$block_class->inner_blocks->rewind();
			?>
	</div>
	<?php

	return ob_get_clean();
}
?>