A default parent router with child routers

Consider the following two classes:

import { Router, RouterConfiguration } from 'aurelia-router';

export class MainPage
{
    router: Router;

    configureRouter(config: RouterConfiguration, router: Router)
    {
        config.map([
            { route: ['', 'entities'], name: 'entities', moduleId: './entities/entities', nav: true, title: 'Entities' },
            { route: 'structures', name: 'structures', moduleId: './structures/structures', nav: true, title: 'Data Structures' },
        ]);

        this.router = router;
    }
}

And

import { Router, RouterConfiguration } from 'aurelia-router';

export class Entities
{
    private router: Router;

    configureRouter(config: RouterConfiguration, router: Router)
    {
        config.map([
            { route: '', name: 'entities-list', moduleId: './list', nav: true, title: 'Entities' },
            { route: 'events', name: 'entity-events', moduleId: './events', nav: true, title: 'Events' },
        ]);

        this.router = router;
    }
}

The problem is that; in a page where the URL reads: http://localhost/ when I execute:

this.router.navigateToRoute('entity-events');

I get the error ERROR [app-router] Error: Route not found: events. But if I change the MainPage class to this:

import { Router, RouterConfiguration } from 'aurelia-router';

export class MainPage
{
    router: Router;

    configureRouter(config: RouterConfiguration, router: Router)
    {
        config.map([
            { route: 'entities', name: 'entities', moduleId: './entities/entities', nav: true, title: 'Entities' },
            { route: 'structures', name: 'structures', moduleId: './structures/structures', nav: true, title: 'Data Structures' },
        ]);

        this.router = router;
    }
}

In a page that URL reads http://localhost/entities, I can successfully execute the given navigateToRoute command. But then I'll lose the root route!

So how can I have a parent router with a default route and some child routes under the default route?

How about using a redirect route to redirect the default route to entities? I'm on mobile right no, so no code sample, but the docs should explain it.