This is the full list of baptisms on the IGI (coverage on the NBI is 1558-1812)
Mary Sanders
Christening: 26 OCT 1817 East Peckham, Kent
Father: Richard Sanders
Mother: Fanny
Frances Saunders
Christening: 23 DEC 1821 East Peckham, Kent
Father: Richard Saunders
Mother: Fanny
Anne Saunders
Christening: 29 JUL 1827 East Peckham, Kent
Father: Richard Saunders Family
Mother: Fanny
Jane Saunders
Christening: 04 APR 1830 East Peckham, Kent
Father: Richard Saunders
Mother: Fanny
Caroline Saunders
Christening: 15 MAR 1835 East Peckham, Kent
Father: Richard Saunders
Mother: Fanny
Elizabeth Tickner Saunders
Christening: 08 JAN 1837 East Peckham, Kent
Father: Richard Saunders
Mother: Fanny
Sarah Ann Saunders
Birth: Snoll Hatch
Christening: 08 JUN 1845 East Peckham, Kent
Father: Richard Saunders
Mother: Fanny
The 1841 census with the children with no baptisms on the IGI in italics (Have you checked the actual parish registers for the missing baptisms)?
1841 census HO107 461/10 folio 13 page 18
Snoll Hatch East Peckham Kent
Richard Sanders 45 Kent Ag lab
Fanny Sanders 45 Kent
Richard Sanders 20 Kent Ag labFanny Sanders 20 Kent
William Sanders 15 Kent
Thomas Sanders 15 Kent Ann Sanders 14 Kent
Jane Sanders 11 Kent
Elizabeth Sanders 5 Kent
Emma Sanders 3 Kent Given the spelling of the surname on the 1841 census and the IGI baptism this birth registration might be the better bet
Births Jun 1845
Sanders Sarah Ann Malling 5 360
FreeBMD isn't sure of the page number a 3 or a 5 but the original looks like a 3 to me - but you need to check it.
http://www.ancestry.co.uk/search/rectype/vital/freebmd/bmd.aspxRegards
Valda