Apple ID family sharing adult birthday got entered as a child! What do I do?

I wrongly entered my teenagers' birthdays! They are over 18 now but we are still on family sharing. I cant change their birthdays so they can't have credit cards etc. Everything they do is connected to their icloud.com email address. How can i resolve this without them having to change their email address and create a new account. I am not at all techy and need help :-)