gp-nested-forms-reorder-display-fields.php

<?php
/**
 * Gravity Perks // Nested Forms // Re-order Display Fields
 * http://gravitywiz.com/documentation/gravity-forms-nested-forms/
 */
// Update "123" to your form ID.
add_filter( 'gform_pre_render_123', function( $form ) {
	foreach( $form['fields'] as &$field ) {
		// Update "2" to your Nested Form field ID.
		if( $field->id = 2 ) {
			// Update "1, 2, 3" to the field IDs from your child form and put them in the desired order.
			$field->gpnfFields = array( 1, 2, 3 );
		}
	}
	return $form;
} );