Cannot add child's apple ID to family account

i am trying to add my daughter to our family account, first its not letting me set her birthday to the actual day in 2008. I can set the year to be 2008 but the only active month and day options are todays date through the end of 2021, nothing before this current years month. Second, when i go to add her email, i get a warning that says that I cannot use this apple ID because it's no longer available...almost like the system is thinking I clicked on the option to create a new ID, and not the section to enter the existing email. This is very frustrating because I have a teen with full rein on this device right now. It seems like something is amiss with my phone, I just upgraded to the iphone13 pro. Any advice?