Hi Chummy,
The steps you are following is correct. We'd like to know which browser are you using when accessing your Microsoft account. If you are using a specific browser only, we'd suggest clearing its cache and cookies then try to go to your account again. You may also try another browser to replicate the issue if clearing cache and cookie didn't help. You should be able to see the Manage my child's profile info under Add a family member. See the picture below for your reference:
Please respond to this thread to let me know how the issue progresses. Similarly, if you have more questions, please inform me by replying to this post.
