FlowBox.get-child-at-pos not working as expected

[hythm7]

Getting this error when running the below code:

No such method 'label' for invocant of type 'GTK::Raw::Types::GtkWidget'
  in block <unit> at /tmp/flowbox-at-pos.p6 line 46

get-child-at-index returns GTK::FlowBoxChild.new
get-child-at-pos returns GTK::Raw::Types::GtkFlowBoxChild.new

use GTK::Raw::Types;
use GTK::Compat::Types;
use GTK::Application;
use GTK::FlowBox;
use GTK::Label;
use GTK::Button;
use GTK::Box;

my $app = GTK::Application.new(
  title  => 'org.genex.test.widget',
  width  => 400,
  height => 400
);

$app.activate.tap({
  #CATCH { default { .message.say; $app.exit } }

  my GTK::Button $exit .= new_with_label: <exit>;
  $exit.clicked.tap: { $app.exit  };

  my $flowbox = GTK::FlowBox.new;

  $flowbox.halign = GTK_ALIGN_START;
  $flowbox.valign = GTK_ALIGN_START;
  $flowbox.homogeneous = True;
  $flowbox.selection-mode = GTK_SELECTION_MULTIPLE;
  $flowbox.min_children_per_line = 4;
  $flowbox.max_children_per_line = 4;

  for 'a' .. 'z' -> $sym {
    my $child = GTK::FlowBoxChild.new;
    $child.add: GTK::Label.new: $sym;
    $flowbox.add: $child;
  }

  #say $flowbox.get-child-at-index( 9 ).get-child.label;

  my $box = GTK::Box.new-vbox();
  $box.pack_start($flowbox, False, False, 0);
  $box.pack_start($exit, False, False, 0);

  $app.window.add: $box;
  $app.show_all;

  say $flowbox.get-child-at-index( 0 ).get-child.label;  # works
  say $flowbox.get-child-at-pos( 0, 0 ).get-child.label; # throws error

});

$app.run;

Edit: remove incorrect statement.