Child Menu in nodered dashboard

[Paul-Reed]

@Talkatoo

When I click any of the menu or sub menu, it disappears from my node read dashboard.

Does it 'disappear' because you have navigated to a different dashboard tab?
If so, that's expected, as you need to install a ui-context node for each menu location.
To avoid duplicating the menu config, save it to context, and allow all of the ui-context nodes to share the single context data (like in this example) .