To solve the ID problem, My family (Wife, DD 4, DS 2.5 and DD 4 months) used large Avery address lables (about 3 x 4 inches) and printed them up on our PC. We stick them under the child's arm, and they stay pretty well. They had the kid's name, the hotel we were staying at, and my cell phone number. My daughter's tag also had big red letters that said "Please don't feed me anything" because she has a servere dairy allergy.
To solve the "what does my kid look like" problem, we all get the same bright colored shirts with a character or picture on them. Assuming that I lose one kid and not all three, I plan to say "he is wearing a shirt just like this one."
We also have these nifty child locators from Fisher Price. You clip one half on the child and the other half on yourself. If they move ouside of a certain range (about 30 ft.) your half starts to beep. There is also a button on the grown-up half which causes the child's half to give off an increasingly louder beep. Finally, the kids half beeps very loudly if it is removed.
They are really neat, but because our kids are so little (6 months littler last trip) they spend most of their time in the strollers and we did not use them much. This next trip (74 days or so!!!!!) we will probably use them more.
BTW, we have current (but not daily) pictures of them also.