Disney tried bands like this year's ago and parents wouldn't need to try to remove them by ripping them.
They would use scissors and reattach them to the shorter kid with tape brought in specifically for this purpose.
This comes up on almost all "How strict are they" threads. What usually happens is then someone will bring up hand stamps. Which then someone will point out that they too can easily be transferred so then more and more complex solutions are suggested including things like photo ids and embedded RFID chips (ok maybe not the last one

). But nothing is as sure as measuring the kid before they get on the ride.