Family Sharing
I cannot link my family's sharing icloud to my childrens phone
Question marked as
Nor should you.
Family Sharing works across different accounts. If your children's Apple ID has already been invited to your Family Group, then they should have access to the iCloud Storage and any other shared subscriptions and purchases.
If not, you will need to invite their accounts. Do not use your own Apple ID on their devices for any reason.
click here ➜ Family Sharing - Apple
and here ➜ Use iCloud+ with your family - Apple Support