I think you may find Thomas appears on the IGI as Thomas HAWKIN, parents "Wm and Hanah" bap 23 Aug 1802 - no other HAWKINs.
SARAH HALKON Christening: 21 SEP 1807 Luddington, Lincoln, England
RACHEL HALKON Christening: 06 MAR 1812 Luddington, Lincoln, England
THOMAS HAWKIN Christening: 23 AUG 1802 Luddington, Lincoln, England
PETER HOLKON- Birth: 10 JUL 1806 Luddington, Lincoln, England
HANNAH HALKON Christening: 13 FEB 1816 Luddington, Lincoln, England
ELIZABETH HALKON Christening: 24 JUL 1817 Luddington, Lincoln, England
MARY HALKON Christening: 17 MAR 1814 Luddington, Lincoln, England
JOHN HALKON Christening: 02 AUG 1798 Luddington, Lincoln, England
WILLIAM HALKON Christening: 21 NOV 1799 Luddington, Lincoln, England
Batches C030031 and C030032
Regarding the date of the marriage, perhaps it was just transcribed wrongly from a faded register ... I've done it myself!