Eventually, someday, I hear this will most definitely be a great way to NOT lose your kids.
In the meantime, you up your chances of the Magic Band working like a safety kit IF you are also staying on Property. I asked the CM who checked up into CBR last time we were there, and she said that our resort information, room number, AND the adult on the reservation all pops up on a resort linked Magic Band...in addition to that child's information that was entered on the reservation associated.
Even that being said, we explained to our kids what to do if they get separated from us. Look for a CM (we told them to look for their CM tags-and/or uniforms!), we used a safety kit as well.