I tend to use the x debugger command, which in some cases makes it more obvious:

  DB<2> x $child
0  Node=HASH(0x1c58f28)
   'parent' => Node=HASH(0x1d9b770)
      'parent' => undef
  DB<3> x $parent
0  Node=HASH(0x1d9b770)
   'parent' => undef
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You can see by the hash addresses that $parent and $child{'parent'} point to the same hash. This is not immediately obvious with Data::Dumper.