Locked out Little sister put the wrong passcode in fifteen times

Maybe you can use iOS Data Eraser to help you erase everything on your iPad. You just need to connect iPad to computer via usb cable, open the iOS Data Eraser tool. After a short time scanning, all data on iPad will be scanned out and displayed on program window Then you can preview and choose them to erase.
iOS Data Eraser Permanently Wipe out Data from iPhone iPad iPod

Is there anything wrong with the passcode? If your iPad is locked and you forget the passcode, please follow the steps below to unlock it.

1.Connect your iPad to your PC or Mac.
2.Select your device in the iTunes sidebar, and click the"Summary" tab.
3.Click "Check for Update". iTunes will show you if there any new version of iPad software is available.
4.Click "Restore iPad". You can finish the restore process by following the instructions given. During the process, a recommend that tells you to back up your files will be given. You can restore your data after the process is complete.

Now, you must have restored your iPad.
Note: Even you bring your iPad to the Apple service center, Apple staff also need to restore your iPad to unlock it. That's to say, you need to erase everything on it.

http://www.leawo.org/tutorial/forgot-ipad-screen-lock-password-how-to-recover-data-from-locked-ipad.html

It really depends if your iPad is locked or not.
Usually you can restore by connecting to a computer and using iTunes.
Follow this easy guide from Apple:
iOS Forgotten passcode or device disabled after entering wrong passcode

iOS Forgotten passcode or device disabled after entering wrong passcode

Interesting question, I looed it up because my memory is so bad I'm likely to forget mine! I only pass coded it to keep the grandkids off it!

See link for instructions from Apple iOS Forgotten passcode or device disabled after entering wrong passcode

If you are locked out, you have to connect to iTunes and do a reset/restore. You can follow these directions from Apple:


iOS Forgotten passcode or device disabled after entering wrong passcode

If you enter the wrong password six times in a row, you will be locked out forever, but you can follow these steps in this Apple article to restore your iPad. This is a security feature to keep sensitive data out of the wrong hands.


iOS Forgotten passcode or device disabled after entering wrong passcode

If you forgot the password then just hard reset it. Here is the method to reset your device:
Hard Reset Procedure For Nook Users

Do a factory reset this will remove any passwords, however it will also wipe all data pictures and so on.

You do not need gmail.com only tap on SETTINGS to factory-reset your tablet.