For me it's simple... the odds are low that Aeralind would be doing that particular activity (i.e. dangerously climbing every vertical surface at a park she's never been too) and there's no way Bronwyn would be doing that particular activity (i.e. sitting quietly and patiently trying to figure out how to play that darn harmonica that B already threw across the room in frustration). Their personalities are different.
Ofcourse, telling you this doesn't make you more able to tell them apart if you haven't spent a good amount of time getting to know each one.
So I thought I'd do a series of visual tutorials.
Telling the Girls Apart: Part 1
Check the hair (if it's down).
For some reason, Aeralind has grown a near perfect set of bangs. I've never cut the front of either girls' hair so it must just be that baby hairs are just starting to grow in front for her. But her hair parts perfectly just left of middle leaving this natural set of bangs.
Bronwyn, however, does not have bangs. Nor does she have a natural part at this time. And if I try to remove the hair from in front of her eyes/nose she throws a fit. Tucking it behind her ears while wet to dry will not tame the mop. And barrettes only last as long as it takes her sister to notice the barrette and yank it out (ouch!). So Bronwyn walks around looking like a shaggy dog.. .and that's okay with her (and me too).