I should add at the moment my kids are quite young under 7yo. But they can use my phone :P

The "why" would be so they are always able to contact me if they need to. It would have no internet and only be used for parental contact... A simple plain phone... just to be able to call me if they need to or for me to call them when they are at their dads...

Tinks - I call them every night they are with him. and he allows that for now. but things are getting rockier!