A major part of Family Sharing is location sharing/tracking. You can use Family Sharing to locate or track a family members' iPhone/iPad. This is convenient in many cases. Fortunately, Apple also has a lot of services already (like Find My iPhone) that match up well with location tracking in Family Sharing.
You can track or locate a family member through Family Sharing in a variety of ways. We've outlined all of them here (if there are other ways, let us know!). Note that Family Sharing can be setup and used via iOS 8 or OS X Yosemite (but you can add any member who's using iPhone/iPad running iOS 7.x too.)
Note: for all this to work, you should have setup Family Sharing and added the members. Here’s a complete guide to Family Sharing in iOS 8.
How to Locate a Family Members' iPhone/iPad via Family Sharing in iOS 8
Option #1. Find My iPhone app
With Find My iPhone, you could track all your devices (all devices that have the same iCloud ID). Starting from iOS 8, you can use the Find My iPhone app to track family members who are part of family sharing.
In the Find My iPhone app, under “All Devices”, your devices are shown first followed by other members' devices. You can tap on each device to check the location along with a few options to play a ringer alert (in case the phone is lost).
Download Find My iPhone
Option #2. Find My Friends app
Find My Friends works pretty similar to Find My iPhone. The only difference is that Find My Friends scans your contacts for iCloud emails and then tracks the location (and shows it on the map). With iOS 8, Find My Friends works with Family Sharing too.
In Find My Friends, you will find a list of all your family members' devices that you can tap on to geolocate on the map.
Option #3. iCloud.com > Find My iPhone
There’s a Find My iPhone web app on iCloud.com. You can use this one to track family members' devices/locations. It works pretty much the same way as the Find My iPhone app. If for some reason you can't use the app on your iPhone/iPad, or a web browser is quickly accessible, just log in to iCloud.com, click on Find My iPhone and you have a map that shows the locations of family members' devices.
Clicking on All Devices lets you pick a device (again, to do things like remotely ring a phone or lock it down).
Option #4. Share via iMessage
It's not necessary that all family members share their locations by default. Since locations are part of privacy, some folks would have disabled this feature. When that happens, you won’t be able to know/track/locate family members’ devices.
But that still doesn't stop the member from sharing their location for a single event. For instance, if you are meeting your spouse/kid somewhere and want a quick update on where they are (for ETA), you can easily have them share their location via iMessage.
Note that this feature requires iMessage to be active (at least in our tests.)