Hi KatieC,
Looking at your previous posts, I take it that the parents are Thomas MCGOWAN and Agnes MCKECHNIE who married in 1845 in Gorbals.
The online IGI lists 8 children for them (including one - Bernard, 20 Aug 1864 - who was registered in both Hutchesontown and Dunoon & Kilmun which seems odd). Of these 8 children, only one is before the introduction of Statutory Registration (1855). So it rather looks as though there may well have been several children between the marriage (in 1845) and the first child recorded in the IGI (in 1854) - possibly including a William?
Do you have the family in the 1851 and 1861 censuses from ScotlandsPeople? If not, these could well include names of earlier children (assuming that there were some) - also, of course, ages and birthplaces.
Regards,
JAP