Hi Oden,
I'm not sure there is a concrete answer out there. I did find a few articles stating 6 graduate schools at Harvard went online this fall. Two of them (Law and Kennedy) offered deferment to any student, no questions asked. I assume the same was offered to HGSE students but can't find that information posted anywhere. The caveat is/was, if too many students defer they risk class of 2022 entrance, not 2021. Are your kids' friends undergrads? I think that' might be a slightly different circumstance if so. There are a host of considerations (networking, finances, experiencing Boston, soaking up Harvard's campus, preferring face to face instruction) that online learning does not support. In other words, don't give up hope! There was a petition among the students population to offer the deferral. Harvard responded well in kind. I don't think they would have offered the second admission cycle unless they needed to fill a statistically significant amount of slots. But agree, still less slots than the first cycle.
Also, there was this interesting article detailing a 2% decrease in endowment funding for graduate programs this year. Before COVID, it looks like most were expecting increased funding. A significant portion of the budget was spent on reacting to COVID (online learning ramp up) even with decreased funding. Which is to say, this is a good year to have healthy tuition revenue. The more admits the merrier?
https://www.harvardmagazine.com/2020/06/harvard-professional-schools-move-online-endowment-distribution-decreased