i had a friend who in the beginning used nail polish on a big toe of each....
alot less expensive than jewelry, and in the 1st week or two they can keep their hospital bands.. ask them if u can borrow a couple more maybe? so when the originals get too tight u can replace them?
and it wont take long for their little individual personalities to show thru.. u wont need to make them identifiable for long.. u will know which is which soon enough
but by all means.. if u wanna get them ID tags then go 4 it..

Seaason

i think its a good idea cos then when they get older they can have something for others to tell them apart