I'd do something else - even just buy different colours for them (so pink for one, yellow for the other) until they were bigger, or use the nail polish idea. To me ear piercing is so permanent. It's like getting a tattoo put on them! I'd not want to do that to anyone unless they WANTED it done. And yes, i'm in the UK where there are 3 week old babies pierced already, but i REALLY don't like that! I know at least 2 babies (one boy, one girl) who have had their studs ripped out in exuberant play as toddlers. Not nice at all!

By the time they are 18mos she'll be able to tell them apart by the way they move, talk, act - their personalities come out alot more once they get a bit bigger.

Bx