Although it does not add Pushpins as direct children of the Map control, MapItemsControl
is what you are looking for:
<m:Map ...>
<m:MapItemsControl ItemsSource="{Binding GPSCoordinates}">
<m:MapItemsControl.ItemTemplate>
<DataTemplate>
<m:Pushpin Location="{Binding}"/>
</DataTemplate>
</m:MapItemsControl.ItemTemplate>
</m:MapItemsControl>
</m:Map>