> if you don‘t want your kids to read your emails, you need to buy them their own iPad.

You're right. But I still think I would buy my kid their own iPad even if my iPhone/iPad had a kid mode. My kid has their own iPad and I still find times when it would be ideal to give them access to the basic features on my phone/ipad. Frankly, if iOS just added the ability to password protect any app then that would be good enough, and it would be useful for more than kids... hand you phone to a coworker or relative to look at photos they can't accidentally/intentionally hop over to your email.