My husband and I went to Walmart and used the dog tag machine and made one for our son that way. They also make Shoe Id tags. And some people use luggage tags or clothing tags.
I'm not sure about any wristband tags though, sorry! Good luck!
We used this, only we found it on Ebay. DD3 wore it on her ankle vs. her wrist. It was REALLY secure and I liked that I could change the info using different cards inside (in case she is with grandparents, cell # changes, etc.) I have seen some that are the rubber bracelets (like the LiveStrong ones) that you have imprinted with your info as well.
But above all that, ensure your child[ren] know to approach a Cast Member as soon as they realize you're lost and ask for help. Cast Members all wear white Disney name tags and are all trained to help kids find their lost parents.
And make sure they understand CMs wear white tags. I always wear a name tag in WDW, but it's not white. I often have parents bring their kids over and say "If you get lost, find someone with a name tag like this and ask for help" . I always correct them that staff only wear white tags.