Oh, new brains when they are uploaded are automatically not public (if that is the question).
From the brains list when you first open a new tab, click the hamburger menu to the bottom right of the brain you want to check, choose Brain access and Sharing, and make sure Allow Public Access isn't checked. Thanks, Zen My understanding is that if all thoughts are marked private AND the brain is marked public, that the public will actually see ONLY the thoughts that are NOT private. But, per other threads (and the notice on the sharing box) any email invites will be able to also see private thoughts. If this is all correct, then marking all as private, but making the brain public, allows you to expose just selected parts of the web brain to the (non-invitee) public. And yes, I think once marked private all children automatically go private. Not sure about siblings.
-- The Cap'n
Surface Pro 4, Windows 10 Dell XPS 15 laptop, Windows 10 Samsung 7Edge