How to use Views Page + Attachment to show parent and children nodes?

I have a site with a node type Lesson, which has a Category field that points to a taxonomy term.

There is another node type Exercise which is a child to a Lesson node.

I previously figured out how to make one view page for a term url that displays both a parent and child nodes. But I was thinking that maybe it is better to have a page view with an attachment, where the page would display a Lesson node’s fields and an attachment would display the children Exercise node’s fields.

The page view has relationship set to taxonomy term and contextual filter set to the category. Then it is set to display Lesson fields.

In the attachment view, parent is set to page, relationship is set to a Lesson reference field. But I have no idea what to choose as contextual filter because there is no filter for me to choose that will get me the lesson id. The attachment doesn’t seem to have a way to get the parent node id (lesson id) from a contextual filter, since the url will only have the term id.

Any ideas on how to make the attachment display the children of the parent that is displayed in the page view?

Thanks!