Find My Friends is the best way to keep track of your family's location. This App allows you to see the current location of your 'Friends' on a map in real-time, pinpointing them quite accurately. These friends can agree to share their location permanently or temporarily.
From within the App you can do a few things that make this app useful for families. You can locate your family members. You can be NOTIFIED when the leave or arrive at a location (great to know they've left school). You can message or FaceTime them from within the App or even get Directions to their current location (so you can pick them up!)
Find my Friends works with any iOS device (iPad, iPad mini, iPhone) and once configured it's always on - assuming their device is either connected to a cellular network or wi-fi zone. Of course it doesn't work if the device is on Airplane Mode, which disconnects the device from all incoming and outgoing signals. But otherwise, it works brilliantly.
I can see it being very useful for people traveling (on vacation) together (with cellular-enabled devices) who want to split up for part of the day but reconvene later on... never wonder why they're a little late, you can see that they're on their way.