Use redirectTo if you using also children parameter, is this possible?

An empty child route should do the job:

  {
    path: 'project/:id',
    component: ProjectComponent,
    children: [
      {
        path: '',
        redirectTo: 'properties',
        pathMatch: 'full'
      },
      {
        path: 'properties',
        component: ProjectPropertiesComponent,
      },
      {
        path: 'stats',
        component: ProjectStatsComponent
      }
    ]
  }