You can use the Windows Phone Toolkit to add children to the map. The Toolkit contains some controls and extensions that make this easier to work with.
<maps:Map x:Name="myMap">
<toolkit:MapExtensions.Children>
<toolkit:UserLocationMarker x:Name="UserLocationMarker" />
<toolkit:Pushpin x:Name="MyPushpin" Content="My Position"></toolkit:Pushpin>
</toolkit:MapExtensions.Children>
</maps:Map>
You can even use templating to bind to a collection of items.
<maps:Map x:Name="myMap">
<toolkit:MapExtensions.Children>
<toolkit:MapItemsControl ItemsSource="{Binding MapItems}">
<toolkit:MapItemsControl.ItemTemplate>
<DataTemplate>
<toolkit:Pushpin GeoCoordinate="{Binding Coordinate}" Content="{Binding Name}" />
</DataTemplate>
</toolkit:MapItemsControl.ItemTemplate>
</toolkit:MapItemsControl>
</toolkit:MapExtensions.Children>
</maps:Map>