So lock your phone every time you set it down. Never leave it unlocked.
I used to have my iPhone lock 5min after I pressed the sleep button. Now that TouchID makes it very easy to unlock, I have it locking immediately.
When I let my friend's 4yo use my iPad, I triple tap the home button and press "Guided Access", which can prevent the user from accessing other apps until I disable it. (I do this because I'm worried about what he may accidentally search on the web, not because I'm worried he'll steal my data!)
I used to have my iPhone lock 5min after I pressed the sleep button. Now that TouchID makes it very easy to unlock, I have it locking immediately.
When I let my friend's 4yo use my iPad, I triple tap the home button and press "Guided Access", which can prevent the user from accessing other apps until I disable it. (I do this because I'm worried about what he may accidentally search on the web, not because I'm worried he'll steal my data!)