Similar for me - it didn't say 'you need to update some info' but instead there was something else in the same place, which required me to verify my identity - once that was done, my family members appeared and I was able to add my daughter's account on this laptop.
This really shouldn't be that difficult - as the user before me said, having a 'click here to sign in so you can see your family' button on the Family & other users screen would be -much- more helpful.
Thank you all for your help.