iCloud Storage not being shared with child under 13

Hello and welcome to Apple Support Communities, juslier,

We understand your son is not appearing in Family Sharing although you've created a child Apple ID. We'd be happy to provide information to help you out.

You may need to invite him to Family Sharing using the steps show here:

Set up Family Sharing - Apple Support

From his device, accept the invitation.

Once he's been added, use the steps outlined here to share your iCloud+ subscription:

Share iCloud+ with your family - Apple Support

"Share iCloud+ with everyone in your family

To share iCloud+, you need iOS 11 or later, iPadOS, or macOS 10.13 High Sierra or later. For the best experience, make sure that your family members' devices meet these requirements, too.

Learn what to do if a family member already has iCloud+

On your iPhone, iPad, or iPod touch

In iOS 16 or iPadOS 16 or later:

1. If you haven't set up Family Sharing yet, set up Family Sharing. 
2. Go to Settings > Family. 
3. Tap Subscriptions.
4. Tap iCloud+.
5. Follow the steps to share your existing plan.
6. Use Messages to let any family members with an existing iCloud+ plan know that they can now switch to your shared iCloud+ plan.

In iOS 15 or iPadOS 15 or earlier:

1. If you haven't set up Family Sharing yet, set up Family Sharing. 
2. Go to Settings > [your name].
3. Tap Family Sharing.
4. Tap iCloud+.
5. Follow the steps to share your existing plan.
6. Use Messages to let any family members with an existing iCloud+ plan know that they can now switch to your shared iCloud+ plan."

Let us know the results.

Have a great day!

juslier,

Does the iPad have the same Apple ID that you created for the child account? Here are a few other areas to check: If you can't find your family's shared content - Apple Support

If it does, then restart the iPad as it can refresh the settings to show the correct plan: Restart your iPad - Apple Support

1. Press and hold either volume button and the top button until the power off slider appears.

2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.

3. To turn your device back on, press and hold the top button until you see the Apple logo.

If you still aren't seeing it, reach out to Apple directly here: Get Support

Take care.