Find my Friends is a useful app for ‘keeping track’ of your fellow iCloud and iPhone users. This isn’t going to appeal to everyone but for parents who would like to know where their young kids are it could be quite reassuring.
Where is my son?
This locates your son, where ever he is (as long as he is with his iPhone).
You can also ask:
Is my wife at work?
Who is here?
Where are all my friends?
Of course the usefulness of this depends very much on how happy people are with other people knowing where they are.