This line in the constructor of Child1Class:

my $self=ParantClass->new();
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creates an object of "ParantClass". In other words, you're only ever dealing with ParantClass objects, while you think you're dealing with Child1Class objects.

You should ALWAYS use the 2 argument form of bless() and use the first argument to the constructor (i.e. the expected classname) as the second argument:

# in the parent class:
sub new {
  my ($class) = @_;
  my $self = bless { },$class;
  # ...
  return $self;
}

# in the child class:
# if you really need to override the constructor
# you can use this:

sub new {
  my ($class) = @_;
  my $self = $class->SUPER::new();  # call parent constructor
  # ....
  return $self;
}
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