You can block unwanted websites on Android phones without using an app by doing this.
On your Android phone, tap the Google app.
Then try to search for anything on the search box.
Look for the More option in the lower right corner and click it.
Go to Settings and choose the General option.
Toggle on the SafeSearch button.
So all inappropriate websites will be blocked on your Android phone. Though kids can learn to undo this in time. So better use mSpy Parental Control.