As a parent with a minor child who has a Facebook account, I'd like to know if there is any way, short of having her show me her privacy settings, that I can detect if my child (friend on Facebook) is blocking parts of her account from me?
You are basically going to have play with your own privacy settings to understand how it works. (A second way would be to compare the appearance of the profile on your account versus a next account , yes ...very obvious)
Once they are signed up there is nothing you can do about it (minor or not)
Some signs that they are blocking you.
For individual wall posts that would be tricky and I would say you are stuck. Someone can comment and provide a suggestion for wallposts.
Of course there's a way: Just ask your child.