This is another instance of the IGI being misleading, many of the entries on there have been added by members of the LDS Church, who's comittment to the church to increase the postumous congreagtion by reasearching their own ancestors, means individuals added to a tree get included, in this case, the Elizabeth Ludlam aged 11 on the 1851 census living as the granddaughter of William and Sophia ludlam, has been included on the IGI as a 'birth' in 1840 to William and Sophia Ludlam. This is of course wrong, as the person adding the info has ignored the relationship status given on the census. there is not apparent baptism for salathiel nor elizabeth included on the IGI, and though i still think that John and Elizabther Ludlem are their parents, it is not provable through baptism and so obtaining the birth certificate is the right choice, I do think however that there will be a non-conformist baptism recorded somewhere for them and the other children,