There were two James Charles, father and son, each with a wife Mary, in Stotfold, one starting to reproduce when his father left off (in fact there was a bit of an overlap). I suspect that you have the younger James, born c 1815 at Stotfold, whose wife Mary was born c1814 at St Pauls Walden, Herts. Unfortunately we only only get one bite of the cherry at her age/birthplace as she was dead by 1861 and James had remarried.
The younger James Charles had a daughter, Sarah, who was 3 in 1841. It looks as though you have the certificate for this child.
Odd, as I can't find a marriage to Mary Brown. Who I assume to be the younger James was married on 8 Nov 1834 at Stotfold to Mary Craft. Unless she was born Mary Brown and had married Mr Craft and was a widow when she married James Charles, but I can't find such a marriage. There's no chance Brown is a badly written Croft?
David