Doug, by 18201210 Frances means bapt 1820-12-10 (year, month, day). In the IGI it reads: GEORGE KERMEEN Christening: 10 DEC 1820 Lezayre, Isle Of Man, Father: GEORGE RADCLIFFE, Mother: ANNE KERMEEN. The IGI always puts the child under the mother's surname even though the actual entry in the Lezayre parish register probably reads something like "George illeg. son of Ann Kermeen & George Radcliffe bapt 10 Dec. 1820". In the IOM at that time most illegitimate children were known by their father's surname. It is possible that there is an entry in the Presentments (held only at the Manx Museum Library - not filmed) which names his parents and his father's requirement to provide for him. Perhaps Frances will look this up for you next time she is in the MM.
If there, this would say what parish his father was from, which would be helpful to confirm that Frances has the right person, because the 1851 census has the George who married Cath Cregeen as b.Andreas (but he might not have known where he was born), and b.Douglas in 1861.

Sue