They need to be downloaded from the App Store as they are not pre-installed. Follow the procedure below to get them.
New devices activated after Sep 1, 2013 and running iOS 7 or later will qualify for the free iWork suite (Pages, Keynote, & Numbers). iPhoto, and iMovie (which are not part of iWork) are also free. If you activated your device before Sep 1, 2013, your device does not qualify.
Try this:
Go here to verify your device registration (you'll need to login using your Apple ID credentials):
https://supportprofile.apple.com/
You can view your registered device(s) here and if there are any you've missed registering, you can do that as well. You can also register new devices here. Afterwards, visit the App Store and your free apps should be available to you.
*IF* this does not work, continue as follows:
Log out of the iTunes Store on your device:
Settings>iTunes & App Store...tap your Apple ID, then select "Sign Out"
Reset your device:
Device Reset (won't affect settings/data/music/apps/etc)
1. Press and hold (& continue to hold) BOTH the Sleep/Wake button & the Home button.
2. Continue to hold BOTH (ignoring any other messages that may show) until you see the Apple logo on the screen.
3. Release BOTH buttons when you see the Apple logo and allow the device to boot normally.
After the device has restarted, sign back in to the App Store as above. Try to download the apps again from the App Store.