Can't be sure which would be the earliest, or even whether these are real memories as distinct from being told about them later, but I would sing Robert Wilson's "A Gordon for me" or Andy Stewart's version of "Coulter's Candy" when about three, so of course I must have heard them... Others which I never sang, but actually do remember hearing my father singing at about the same time, would be various ones of Burns's, Barnes's "Linden Lea", and the ballad about "A Cherry without a Stone" &c.