I think the real problem is that parents want to use a phone or tablet as a pacifier, so they don't have to parent the tykes.
Ah yes, the rallying call of the childless. I'm sure that if you ever have kids, you'll have the means and inclination to devote N hours of your own time every day simply to keeping them entertained.
I have kids of my own, and we also have several tablets, two iPhones (my wife and I each have one), and many gadgets in the house. However, we don't mix tablets/phones in the sense that if I ever have to enter a password into a tablet, that particular tablet does not ever get used by the kids. But you don't need to even have separate tablets (i.e. one for you and one for them). If they ever ask me to enter a password, the answer is no. When my toddler plays with my phone, I make sure that it won't ever get messed up when I get it back from him by taking precautionary steps (e.g. turn off emails, make sure everything requires passwords, etc.) I don't just hand them the device and cry to Apple when they break it.
Then there's also the question of "keeping your kids entertained." You don't need to devote hours of your own time. There are myriad types of toys to entertain your kids -- and even educate them while they're playing. If your tablet is causing problems, then perhaps they could use something else as edutainment. Get them puzzles, coloring books, reading books, etc.