package Parent;
use Child;
sub new {
   my $that  = shift;
   my $class = ref($that) || $that;
   my $self = {
      children=>undef;
   };
   bless($self, $class);
   $self->init();
   return $self;
}
sub init {
   my $xmax=5;
   my $ymax=5;
   foreach my $x (0 .. $xmax) {
      foreach my $y (0 .. $ymax) {
         $self->{'children'}[$x][$y]=Child->new($self);
      }
   }
}

package Child;
use Parent;
sub new {
   my $that  = shift;
   my $class = ref($that) || $that;
   my $parent = shift;
   my $self = { 
      parent => \$parent;
   };
   bless($self, $class);
   return $self;
}
sub whereami {
   #i don't know how to ask the parent here;
}