In that example you're not actually sharing the data: you're creating a new hash every time data() is called. If you really want to share the data, you can do:

my $data = { one => 1, two => 2 }; 
sub data { return $data; }
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I don't know how you'd use tie() to get the original code to work. If you really want that construct, you'll need to use symbolic references or - even more dangerous - eval.

Also note that even if it would work as you expected, the original code will break as soon as someone subclasses Child.

update: in the example you posted here, there's no need to do

my $proto = ref $self;
print $proto->data;
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You can just call

print $self->data;
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