Hilariously, there's actually nothing stopping the kid phoning whoever they want. It's controlled by a contact group on the phone, that the child device can edit at will. Step 1 would be to add all friends to that group.
Ha. I guess I'll put it on my son's phone and tell him that there is a "solution" to fully defeat the app. Make a game out of it. (and I'll tell him Mom won't know)
PS this is how you build trust with your kids.