Press and hold the sleep/wake button. When the slider appears, drag it, and turn off your device. Press the same button again, and turn on your device.
Another reason why the app is crashing may be the fact it needs to be updated. Go to the App store, find Google maps, and if the update is available, download it.
This is also a simple solution. What you need to do is delete the app from your phone, and then install it again. To delete the app, find its icon on the Home screen, press and hold your finger on the icon until an X appears. Click on it, and the app will be deleted. Go to the App store, find Google maps, download and install it.
Make sure that you have the latest version of iOS on your device. If not, download and install it, and that will probably fix the problem with the app, including some other device glitches.
Before you start with this task, make sure to back up all your files to iCloud. Navigate to Settings > General > Reset > Erase all Content and Settings. Once the process is done, you will have to set up your device as new, following the given steps.