I am giving my 5yr old an iPad of his own. I'm happy to buy and share apps with him but how do I keep our text messages and emails separate?
You can logout from iMessage and the Mail app (or don't even log in with your accounts to start with).
To turn messages and email off you can do the following:
iMessage: Settings > Messages > iMessage OFF.
Mail: Settings > Mail, contacts, calendars > the email account > off or delete account.
You can still use your Apple ID on that iPad for the store account.
If you just want to turn of notifications of mail and iMessage you can do that in the notification centre under settings.