Delete My Gmail Account In My iPad
Just remove the Gmail account from the iPad by going to Settings -> Mail, Contacts, Calendars -> Select your Gmail account -> Tap the Delete Account button. 

The account will no longer be available on that iPad, but no contacts or email will be deleted from the account at Google, just from the iPad. DO NOT delete the emails and contacts themselves manually, they will be removed from the iPad when you remove the account from it.

Depending on the age of your kid and how much you want to keep him/her from getting access to your emails and contacts, it might also be enough to just disable Mail, Contacts, Calendars and/or Notes from the Gmail account screen instead of removing the entire account. If you do this, just enabling them again will put the email and contacts back on the device.