Chances are, if your child can hold a pencil, they already know how to use a touch screen and love watching videos on YouTube.
If you browse to Kids.YouTube.com, you will find YouTube (owned by Google) offers a much more kid-friendly "YouTube Kids" app on iOS and Android.
The app is cast-enabled, for those with Apple TV, Chromecast, game consoles or a smart TV. Despite its added safety, parental supervision may be necessary.
Filtered content: YouTube Kids app allows only videos and channels appropriate for children. If you use the built-in parental controls (password protected) you can turn off search, activate a timer to limit screen time, and disable background music or sound effects. A Google account is not required, but the app still tracks videos watched to recommend new videos to watch. If you keep search on, inappropriate search terms like "sex" will be blocked. YouTube advises users to flag content that is inappropriate. Adult-level features like user comments and uploading videos are removed entirely.
Filtered ads, with no click-throughs: A YouTube spokesperson told The Guardian, "We only show ads [in YouTube Kids app] that are approved as family-friendly – for example, we don't show any food and beverage ads – and all ads undergo a rigorous review process for compliance with our policies. All ads are clearly labelled and include ad intros. Ads don't include any click-throughs to websites or product purchase flows."
QUICKLY RESTRICT ANDROID DEVICE TO ONE APP
If you have an Android 5 (Lollipop) device, you can turn on "App Pinning" to lock your device to only one app. To turn the feature on, tap on the "Overview" (two squares) recent apps button, then tap on the "Pin" settings icon (bottom of the screen). Move the slider for "App Pinning" to on.
Use App Pinning by tapping on the "Overview" button again, then tap on the Pin icon on the app's preview.
If you have Android 4.3 or above, you can set up a new User account in Settings, and set it as a "Restricted User", to disable access to apps and restrict content settings. Activate that account before your child uses your device.
iOS PARENTAL CONTROLS
In the iOS "Restrictions" settings, you can disable certain apps, toggle any feature and restrict content ratings. In iOS Settings, go to General, then Restrictions. Enter a new Passcode. You can also set a volume limit and turn off mobile data.
There is also Guided Access, to restrict use to one single app. Go to General > Accessibility > Guided Access. Don't forget to set a Passcode. Enable the shortcut to turn it on (or off), which is three quick clicks on the Home button.