It is NOT a good idea to put your child's name anywhere that it can be seen. That is an invitation to a predator to call them by name, making them familiar to them.
While it's too late for the OP's trip, I bought military style dogtags (
www.gotags.com) for my DDs with their name, our names, cell and home numbers on them. On the back, I put a label with our resort name (which can be changed for different trips). I also recently ordered them silicone bacelets (
www.rekeydesigns.com) with Mom: (cell number) and Dad: (cell number) engraved on them. They wear these all the time now.
for the OP, when you get to the park, show your older 2 a CM name badge and tell them to look for one of those if they ever get lost. Also, you can make up labels for the INSIDE of their shirt (at the hemline) with their name/info on it and instruct them to show that to a CM if they are ever seperated from you.