"Resetting" the iPad is different than restoring it to factory settings and that is what you have to do if you forget the restrictions passcode. Restoring from a backup (if the backup contains the passcode) will not do any good since you will be restoring the passcode back onto the iPad, so restore the iPad as new and start all over again.
See of either of these methods will work for you. You will be erasing the device completely with both of theses methods as well.
If you have Find My iPhone enabled, you can use Remote Wipe to erase the contents of your device. If you have been using iCloud to back up, you may be able to restore the most recent backup to reset the passcode after the device has been erased.
Alternatively, place the device in recovery mode and restore it to erase the device:
- Disconnect the USB cable from the device, but leave the other end of the cable connected to your computer's USB port.
- Turn off the device: Press and hold the Sleep/Wake button for a few seconds until the red slider appears, then slide the slider. Wait for the device to shut down.
- While pressing and holding the Home button, reconnect the USB cable to the device. The device should turn on.
- Continue holding the Home button until you see the Connect to iTunes screen.
- iTunes will alert you that it has detected a device in recovery mode. Click OK, and then restore the device.
Coped from here.