Xamarin Forms: ContentPages in TabbedPage

As on date today, it's not necessary to add "Children" property. If your Pages are in another directory say "PagesDirectory". You can reference the content page "Page1" as below, it will work absolutely fine:

 <TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         xmlns:d="http://xamarin.com/schemas/2014/forms/design"
         xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
        xmlns:views="clr-namespace:YourApp.Views.PagesDirectory"
         mc:Ignorable="d"
         x:Class="YourApp.Views.TabbedPage"
        Title="Tabbed Page">

<views:Page1 Title="Content Page 1"></views:Page1>
<views:Page2 Title="Content Page 2"></views:Page2>

You are doing it wrong. You must place the pages as the TabbedPage Children.

Here is the solution:

<?xml version="1.0" encoding="utf-8" ?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
            xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
            xmlns:mypages="clr-namespace:MyApp.Pages;assembly=MyApp"
            x:Class="MyApp.Pages.Navigation">
  <TabbedPage.Children>
    <mypages:Page1 Title="Home"/>
    <mypages:Page2 Title="Browse"/>
  </TabbedPage.Children>
</TabbedPage>

In alternative you can do it programmatically:

public class TabsPage : TabbedPage
{
    public TabsPage ()
    {
        this.Children.Add (new Page1 () { Title = "Home" });
        this.Children.Add (new Page2 () { Title = "Browse" });
    }
}