Sharing iCloud+ subscription not working for child account

Hello,

I have 200GB iCloud+. I have enabled sharing with my family members T (adult) and N (child). For N, on my side, it says "Not Using". When I go to N's phone, it will not allow me to enable it on her side. I have read to remove a family member and re-add them should fix the problem, but I cannot remove N as they are a child account and require an adult.