Audrey,

I extracted the SEWELL baptisms, marriages, and burials from the St. Cuthbert's parish registers microfilm 1813-1830 (LDS film number 90579). I think these baptismal entries may pertain to your line of the SEWELL family (all spellings exactly as they appeared in the register):

Page No. 60, Baptized October 1, 1815, Entry No. 478, Christian Name Sarah, John & Mary Sewell, St. Cuthbert's Lane, Weaver, J. Fawcett, Curate

Page No. 83, Baptized September 15, 1816, Entry No. 664, Christian Name Mary, John & Mary Sewell, St. Cuthbert's Lane, Weaver, William T. Briggs, Lecturer

Page No. (None), Baptized November 7, 1819, Entry No. 1236, Christian Name Ann, John & Mary Sewel, St. Cuthbert's Lane, Weaver, J. Fawcett, Curate

The birth of son William would have pre-dated this microfilm, and I did not see the birth of son John. If his age was rounded up on the 1841 Census, it's possible his birth was after the cut-off of the microfilm. I'll have a look again when I go back just to make sure I didn't miss it.

Hope this helps! If you'd like a copy of my entire file of SEWELL entries from this microfilm, I'd be more than happy to share it with you. I did my best so hopefully there are no omissions or misspellings.
Lisa