Good luck. I'm told that the gaps in Walcot are 1801-1818, 1822-24, 1832-34 but that the work is ongoing and gaps should be filled soon.
Those are actually the gaps in the burial transcriptions. The baptism transcriptions have fewer gaps but still some. They can be obtained by joining the Yahoo group for the Bath Forum Hundred (i.e. Bath and surrounding parishes)
http://uk.groups.yahoo.com/group/bathforumhundred/St Swithin Baptisms 1832 - 1837.xls Transcribed by Tony Evans 470 KB Sep 24, 2009
St Swithin Baptisms Feb 1863- 2 Jun 1867.xls Transcribed by Tony Evans 265 KB Aug 10, 2009
St Swithins Baptisms 2 Jun 1867- 4 Jan 1872.xls Transcribed by Tony Evans 284 KB Jan 4, 2010
Walcot St Swithin baptisms 07Apr1830-06Apr1831.xls Transcribed by Karen Hailstone 404 KB Jul 31, 2009
Walcot St Swithin baptisms 1773-1779.xls Transcribed by Anne Davis 608 KB Jan 1, 2009
Walcot St Swithin baptisms 1801-1819revised.xls Transcribed by Trish Jamieson , Sheilia Ferris ,Gerald Goode, Vicki Danielson,
and Christine Bennett 3110 KB Jul 24, 2009
Walcot St Swithin Baptisms 1827-Apr1830rev.xls Transcribed by Sheilia Ferris, Mary Robinson, & Andy Phillips 918 KB Jul 24, 2009
Walcot St Swithin baptisms May 1835 - 1837.xls Transcribed by Grace Wilmott, Karen Bradley, Jeanne Winters
& Christine Bennett 314 KB Jan 2, 2009
Walcot St Swithin baptisms Nov 1820 1824.xls Transcribed by Christine Bennett 471 KB Nov 27, 2008
Walcot St Swithins Baptisms 9 Dec 1838-15 Mar 1840.xls Transcribed by Tony Evans 179 KB May 28, 2010
Walcot St Swithins Baptisms April 1831-1 Jan 1832.xls Transcribed by Tony Evans 119 KB Feb 26, 2010
FreeREG uses the same transcriptions but it can be helpful to have the whole files. You can do more cpmplex searches or even read them right through. You might spot an unusual spelling which a Soundex search missed.
Having said that, I can't see any variation of Izatt in the files for 1820-40. It would be unlikley that all the children fell into the gaps, suggesting they lived elsewhere or they were non-conformists.
David
Oops, I didn't look very carefully, there is one at Walcot:
25 Jun 1837 Samuel M James Harriett IZETT
There is also this baptism at Weston (a village on the edge of Bath):
24 Jan 1836 John m James Harriet IZETT Weston Pensioner
but I see you've already found them.