Jiovann,
Thanks for posting here in Apple Support Communities. Are you seeing the account in your Family Sharing group in Settings? Check out this link that will help to ensure that you've got Family Sharing set up properly so that your child can have access to the iCloud storage as well and let us know if this helps: Share iCloud+ with your family - Apple Support
"In iOS 16 or iPadOS 16 or later:
- If you haven't set up Family Sharing yet, set up Family Sharing.
- Go to Settings > Family.
- Tap Subscriptions.
- Tap iCloud+.
- Follow the steps to share your existing plan.
- 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:
- If you haven't set up Family Sharing yet, set up Family Sharing.
- Go to Settings > [your name].
- Tap Family Sharing.
- Tap iCloud+.
- Follow the steps to share your existing plan.
- Use Messages to let any family members with an existing iCloud+ plan know that they can now switch to your shared iCloud+ plan."
Kind regards.