ansaction
        "transactionid",    (string) parent transaction id
       ... ]
    "spentby" : [           (array) unconfirmed transactions spending outputs from this transaction
        "transactionid",    (string) child transaction id
       ... ]
    "bip125-replaceable" : true|false,  (boolean) Whether this transaction could be replaced due to BIP125 (replace-by-fee)
  }, ...
}

Examples:
> bitcoin-cli getmempooldescendants "mytxid"
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"cur