Here's a great little gizmo for kids in Korea and Japan by KDDI. It's a cellphone made just for kids. Here are some of the great functions of this phone:
It has a function called SECOM, which I believe is like 911. See what happens when the SECOM button is pushed:
It also has an emergency light that comes on when it senses darkness, earthquake alert, GPS (location of your child). Another great feature is that the child can only contact people in their contact list (up to 4 contacts) via phone or email.
Your children will not have internet access on the phone.