You're definitely pointed in the right direction on the origins of DeRosey Carroll.I've been researching the Carroll family that lived at Susquehanna in St. Mary's County, Maryland.The Carroll family here was part of St. Nicholas Church, whose first full-time paster was Sebastian DeRosey, which it appears is who DeRosey Carroll is named after.The lineage for this Carroll family can be found at http://genforum.genealogy.com/carroll/messages/8172.htmlhttp://genforum.genealogy.com/carroll/messages/8172.html
I haven't found anything to verify that DeRosey was Charles J. Carroll's son, but it would be my best guess that he is.
Here is a reference for a record at the Maryland Archives that includes DeRosey and the rest of Charles' children: CHANCERY COURT (Chancery Papers) 1826/03/04 6412: Joseph N. Burch vs. John B. Brooke, Araminta Brooke, Eleanor Beans, Eleanor Whitaker, John H. Carroll, Sophia Carroll, Derosa Carroll, Michael Carroll, Amelia Whitaker, Charles J. Carroll, Harriett Brooke, George Carroll, and Celestia Whitaker. PG. Title to Mount Calvert Manor, Bealls Gift. Recorded (Chancery Record) 150, p. 125. Accession No: 17,898-6412-1/9. MSA S512-64721/37/3/
I feel as though I've seen more records including DeRosey with this line of Carrolls, but none are coming to mind right now.
In case you're interested, a little extra on Sebastian DeRosey from http://www.mdscv.org/1836/dispatch.pdfhttp://www.mdscv.org/1836/dispatch.pdf: "Rev. Sebastian DeRosey was a French Capuchin monk on board a French ship during the Blockade of the Chesapeake Bay. At the end of the War, he remained in St. Mary’s and acted as Pastor to the people of St. Nicholas. He died Christmas day, 1812 and is buried under the nave of the original church."