Blueprint - Label for Nested blocks (Number of items)

How do I display the number of Nested items inside a block in my label?

Basically I have a block, with nested blocks inside. I want to display to the user how many items are in that block before they click to edit it? ie:

name: Icon grid
label: “{{ block.subitems.count }}”

Something like the examples here should work: Modifying blocks types and custom blocks | Kirby CMS

i.e. name_of_nested_blocks_field.length