Seconds can be very valuable in a dangerous situation.
Having a pre-programmed phone buys your child enough time to alert 911. When a door is being pushed open by someone bigger than your child, your child needs immediate help, they may not get the opportunity to hit 3 numbers and 91 won't do them much good. When you pre-program your phone choose a setting that won't constantly be set off accidentally, this is important. Also, stress to your child that 911 is for emergencies only and that is anytime that their physical safety is being threatened. Please stress to your child that most people are good, there are however people that have been known to harm children, we are only taking precautions just incase they should ever come across one of these people.