Because if the kitty were to repeatedly scratch or bite your granddaughter, they would be kept separate so that could not happen again. Common sense. Repeated injuries coinciding with a person/animal/location/activity should be prevented. By eliminating whatever the cause of the repeated injury is. Certainly there are times that's not possible. Like a child with an overbite might repeatedly bite their lip. However if they are repeatedly biting their lip because they fell down while tripping over garbage on the floor.... that can be at least reduced by cleaning up. Absolutely kids should be kids. However, precautions should be taken to ensure they survive being kids.