I was writing this code while you were posting...

use strict;
use warnings;

package Foo;
use parent 'Foo_Bar';
sub new {
    my $class = shift;
    return bless {}, $class;
}
sub aa {
  my ( $self, $args ) = @_;
  my $val = $self->_aa ( $args->{'bar'} );
  print "aa\n";
}

package main;
my $foo = Foo->new();
$foo->aa( { arg1 => 'some' } );
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and in Foo_Bar.pm (underscore instead of :: only for my convenience):

use strict;
use warnings;

package Foo_Bar;
sub _aa {
  my( $self, $quux ) = @_;
  print "\t_aa\n";
}
1;
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