On Page Menu for Modular Page with Modular Children

Hi,

New to Grav and still trying to get a grasp on menu creation.

I the below setup as a really long single modular page broken down into chapters and sections.

The only problem is the on page menu is currently only showing the parents in the modular collection and not the children. The active menu items appear to be drop downs but they are just the single parent.

Thanks!