Parental Controls on iOS are extremely helpful for parents of iOS-device-using kids. They allow a parent to block in-app purchases, restrict explicit content on the device and block apps that are not needed for younger children (Mail, Safari, etc.).
Setting up these restrictions requires a special 4-digit PIN that only needs to be entered when a parent makes changes to the parental control settings. Because the code is entered so infrequently, it is easy to forget the password, especially if you set up restrictions in haste and don't take the time to record the code in your favorite password keeper. This happened to me recently, and I will give you a few tips on what to do if you find yourself in this unfortunate situation.
Assess and Review
If you realize that you have forgotten your parental control password, don't panic. The first thing you should do is stop entering password guesses, as iOS will lock you out of parental controls when you hit five incorrect password attempts. After the fifth try, you have to wait for a minute before you can try again. This wait time goes up to five minutes, 15 minutes and eventually an hour, which can be very inconvenient if you find the password written down on some loose post-it note in your junk drawer.
If you can't find that lost password anywhere, then you have two choices to fix the problem -- you can either wipe your phone and start from scratch, or try to reset the password by careful editing of system files. I prefer the former solution, but will present the latter for those who are comfortable with hex editors and SHA-1 hashes.
Perform a Factory Restore
In my opinion, your best option is to wipe the device completely and perform a factory restore. You will lose the photos, notes and other personal information on the device, but you already had those backed up via iTunes sync, in iCloud, Photo Stream or other services like Dropbox, right?
You have to restore the iOS device back to factory settings and can't restore using an iTunes backup, as all the backups contain your parental control password along with your photos and app data. Forget about any saved backups and set up your iPhone or iPad as a new device within iTunes. You can restore your iOS device to factory settings using iTunes and this handy guide from Apple. Keep in mind this will also blow up any game progress or other customizations, so be prepared for that conversation with the younger users of the device.
When your device is restored, you can connect to iCloud and download your notes, bookmarks and other data. You will have to configure any email accounts and re-install all your apps. It's a pain in the neck to do this, but it is the safest solution to get parental controls back and running.
Recover the Password by Editing System Files
If you are very tech savvy and don't mind a slight risk of bricking your device, you can edit a few system files and either find the parental control password or reset it. These two procedures assume you are using a Mac or a PC to backup your device and the backups are not encrypted.
If you happen to have an older iOS device that hasn't been updated to iOS 6, you can use these directions from Simon Blog to locate the parental controls password in a system file (com.apple.springboard.plist) that is stored in a backup on your desktop machine. I tested this on a very old (and now abandoned) iPod touch that is still running iOS 4.1, and it works. The PIN is stored as a string and can be found without touching your iOS device.
If your device is on iOS 6 or later versions of iOS 5, you may have to dig a bit deeper to unlock the parental control password. In recent versions of iOS, Apple removed the parental control PIN and now keeps it hidden from prying eyes. You can no longer read it as a string, but you can force iOS to change it using a few carefully placed lines of code.
The detailed process of resetting your parental control password is explained by iPhone Backup Extractor and requires you to locate a recent iTunes backup from the iOS device. You then edit the com.apple.springboard.plist file and the manifest.db file in the backup, and enter in a new parental control password that overwrites the old one. To send those password changes over to your device, you must restore your device in iTunes using the backup that you just modified. If successful, you will have a new Parental Control password that you can easily enter.
The process is straightforward, but it requires you to know how to use a hex editor and understand a bit about SHA-1 hashes. I tried this technique twice -- once on an iPad mini running iOS 6.0.2 and once on an iPad running iOS 6.1.3. Both times it did work, and I was able to change my parental control password to 1234.
I have to admit that it was a bit nerve-wracking, especially during the restore process, as I was concerned that the smallest mistake would foul up my device. Though I don't recommend this process, I present it for those who are desperate and don't mind the risk if it means preserving that important game save, photo or document.