How to make an antonym for a tag in php?

Question

PHP

There is a tag
[isparent] текст [/isparent]
This tag displays the text contained in them if the category is a parent category and contains subcategories.
His code:

if(!isset($row['children'])) {
  $template = str_replace( "{sub-item}", "", $template );
  $template = preg_replace( "'\\[isparent\\](.+?)\\[/isparent\\]'si", "", $template );
} else {
  $template = str_replace( "[isparent]", "", $template );
  $template = str_replace( "[/isparent]", "", $template );
}

How to do the complete opposite?
[isnotparent] текст [/isnotparent]

For a tag to output content if it's not a parent?