Google Calendar not syncing with iOS 7 (tried deleting account, creating Google or CalDAV, nothing worked)
Go to https://www.google.com/calendar/syncselect and make sure that you have all of the calendars enabled.

See https://support.google.com/calendar/answer/151674 for more information --- However!  Be sure to ignore the part about Google Apps unless you have a paid Google Apps account. Specifically do not use https://m.google.com/sync/settings/ unless you are using a paid Google Apps account.)

http://productforums.google.com/d/msg/calendar/G4ClHD46kP4/LekDrZoyCo0J is also helpful to understand the changes that happened when Google switched from Exchange ActiveSync to CalDAV. The author of that posts suggests https://www.google.com/calendar/iphoneselect and/or
https://www.google.com/calendar/hosted/YOUR.DOMAIN.HERE/iphoneselect
(the latter being for Google Apps hosted accounts). In my experience they all seem to lead to the same place, but YMMV.

If you have more than one Google Apps/Gmail account, but sure to log into the right one before you try any of this.

Last but not least, you may need to 'force quit' the calendar app on the iOS device (in iOS7, double-press the 'Home' button, then 'flick' the app off the top of the screen). My suggestion would be to start by deleting the Google account from your iOS device, then go and enable the CalDAV settings, and then re-enable the Google Account. That should give everything enough time to re-sync and notice the changes.