Get children of parent page

How can I get the children of a parent post (page)?

For example in a default install I have a page (ID 2) and created a new page as a child of this (ID 3). I want to pass ID 2 and get the parent and all children back.

How can I do this?

Obviously I can get the parent itself with:
https://127.0.0.1/wordpress/wp-json/posts/2

(I am actually looking to do this with bbPress CPT topics which are parents of CPT replies – but I figure if I can’t get it working with standard pages I’ll never get it working with bbPress).

Thanks.

https://www.ads-software.com/plugins/json-rest-api/