Kid.pm (parent)
------
package Kid;

sub new
{
bless ....
}

sub getSex
{
	print("I am unisex \n");
}


Son.pm
------
package Kid::Son;
@ISA = qw(Kid);
use Kid;

sub getSex
{
	print("I am a boy \n");
}

Daugther.pm
-----------
package Kid::Daugther;
@ISA = qw(Kid);
use Kid;

sub getSex
{
	print("I am a girl \n");
}


test.pl
-------
#!/usr/bin/perl

use Kid;
use Kid::Son;
use Kid::Daugther;

# Create Instances
$kid = Kid->new();
$son = Kid::Son->new();

# 1. Its OK
$kid->getSex();

# 2. Its OK too
$son->getSex();

# 3. Its not OK
$kid->son->getSex(); # I know its wrong !