If you have kids, chances are they've gotten into your phone to play games. Since most of our phones aren't exactly set up for children, it's easy for them to get into things they shouldn't. This is why it may be a good idea to set them up with a device specifically for them.
An Android phone is probably the best option because they're highly customizable and very inexpensive compared to other devices aimed at children. The Samsung Galaxy Rush is a good example of a phone that's under $100, runs Android 4.0, and has a front-facing camera.
It's also a good idea to put a bunch of kid's movies and shows on the phone. You can even put shortcuts to files directly from the home screen using ES File Explorer. GoLauncher Ex will then allow you to change the image for those icons so they will be more visual.
Lastly, set the device to Airplane Mode so it can't get online. It would also be a great idea to get a case for it since it will likely end up airbourne. For more details and a video walk-through of how to do this, watch episode 28 of Know How.
Children under a certain age can't have Google accounts. We don't recommend using your own Google account with your child's phone to prevent accidental purchases.