Here is the way to turn on Content Blockers to FamiSafe Jr on kid's iOS devices.
1. Go to Settings on your kid's device.
2. Scroll down and tap Safari.
3. Tap Content Blockers under Safari.
4. To activate Content Blockers, toggle the switches next to FamiSafe Jr to the green ON position.
If this option is greyed out, you need to activate Content Blockers first:
1. Go to Settings > General > Restrictions and enter in your passcode.
2. Scroll down to the Allowed Content section. Do you have any restrictions set for websites other.
than All? If so, you'll need to disable them in order to activate your content blockers. (Alternatively, just turn Restrictions Off.)