MotherClass
                  /   \
                 /     \
                /       \
        ChildClass1   ChildClass2

##</code><code>##

package MotherClass::ChildClass1;

use strict;
use vars qw/@ISA/;

use MotherClass;
@ISA = qw/MotherClass/;

sub new {
   my ($class, $args) = @_;
   my $self = $class->SUPER::new($args);
   ...
}

##</code><code>##

package MotherClass::ChildClass2;

use strict;
use vars qw/@ISA/;

use MotherClass;
@ISA = qw/MotherClass/;

use MotherClass::ChildClass1;

...

sub object_method { MotherClass::ChildClass1::object_method(@_) }