I have the child tattoos & that will work well- I like that more than a wrist band, bc it stands out more- people will expect the kids to have wristbands on & may not look at them closely. I also am going to try a "child locator" this year- don't know yet, but here's an amazon link:
http://www.amazon.com/gp/product/B0009PLRXKOther than that- the fest is so kid friendly, people are pretty on the lookout for stray little ones. The one thing we have going for us is that a toddler DEFINITELY looks out of place without an adult scrambling after them! Good luck
Jen