You and I seem to be looking at different records! The only Thomas Moore son I saw was bapt in German like all the other children, except for the one in Rushen who had no mother's surname and was probably from a different family:
Thomas Moore
Isle of Man Parish Registers, 1598-2009
christening: 9 April 1815 German, Isle of Man
father: Thos Moore
mother: Elinor Kneen.
Plus:
Jane Moore
Isle of Man Parish Registers, 1598-2009
christening: 3 August 1823 German, Isle of Man
father: Thomas Moore
mother: Elinor Kneen

Elizabeth Moore
Isle of Man Parish Registers, 1598-2009
christening: 12 March 1826 German, Isle of Man
father: Thomas Moore
mother: Elinor Kneen

William Moore
Isle of Man Parish Registers, 1598-2009
christening: 4 July 1830 German, Isle of Man
father: Thomas Moore
mother: Eleanor Kneen

Robert Moore
Isle of Man Parish Registers, 1598-2009
christening: 30 December 1832 German, Isle of Man
father: Thomas Moore
mother: Eleanor Kneen

John Moore
Isle of Man Parish Registers, 1598-2009
christening: 23 May 1813 German, Isle of Man
father: Thos Moore
mother: Elinor Kneen

Margaret Moores
Isle of Man Parish Registers, 1598-2009
christening: 6 December 1835 German, Isle of Man
father: Thomas Moores
mother: Eleanor Kneen

There was also the one in German with mother's surname Kneal which could have been a clerk's error.

Sue