Leave it on the front. If he were to get separated, and be upset, he may not (and probly won't) be able to comprehend what's going on. If a CM were to ask some questions as to... are you lost? is this number here for your mommy or daddy? he could shake his head or whatever and they could call. As others have said, if CM's aren't allowed to search for info, you need to have it readily available to them. Granted it's not your kid, but he'd be getting help (answering to if it's mom or dad's number).
Just make it a Disney themed button so that it fits in with the first visit button. And being if they get lost, Adventure is out there!
it'll fit perfectly.