If you've searched for baby clothes in Google there's absolutely nothing in the FLoC proposal that stops Google from inferring that you're a parent from that search and, idk, storing a bit in your profile or something.
This proposal is about allowing ad targeting to interests or whatever without tracking your visits across the web - your browser generates the cohorts clientside (idk how the cohort assignment algorithms get standardised on, I guess that's where the 'tuning' would go). And yes, you could just tell your browser not to do that, or have it only use the most recent n days' data, or randomize your cohort, or freeze your cohort in time, or blocklist certain sites from ever entering your cohort, and so on.
Where this ties into tracking if you're a parent is that while it doesn't prevent tracking that, it does lessen the incentive - if you're a parent, you're likely going to wind up in a parent-y cohort. Is the signal from the original search still going to be useful enough to warrant keeping around?
(obligatory: googler, but nothing to do with ads)