A 'possible' marriage is Q2 1910, Gateshead, but the index for that gives a choice of two brides with the first name Margaret. Either Margaret GIBSON or Margaret WHITFIELD. Looking at online trees Margaret WHITFIELD married a man with the surname LOTINGA, so it looks more likely that 'your' Margaret was Margaret GIBSON.
(though that is just a working theory to be explored, not writ in stone)
Do you know of any other children born since that census?
After Sep 1911 the GRO index included mother's maiden name in the births register.
Other than that, the birth cert for the son on that census return would give you the info you are looking for.
Boo
