Just to add a snippet to Guy's excellent reply ...
The IGI on FamilySearch is often incomplete. For instance, there are many instances where only the girls have been extracted from the Church Register into the online IGI - although, of course, there is the normal complement of boys and girls in the actual records.
The Scottish Church Records CD which the LDS FHC's have available for consultation includes the boys as well - and often fills in other gaps.
JAP