A few points:
1. Their argument basically boils down to these vague notions of mental health/well being. You can't weigh that against a tangible pandemic that is literally killing people, and even many that survive are having serious long term effects. The idea that "The trauma that kids are going through not socializing and being in school is a greater social health concern than the virus" is insane. On no planet is that true, but especially not in an America that has failed to do what it needs to at every turn. EVERY turn. We have allowed a very dangerous public health situation to unfold and sending millions marching right out into an environment that is likely to allow it to propagate unchecked is wildly irresponsible.
2. Let's say that we all go back in a month or two. It's going to vary by district and state, but a lot of places are going to look like this: no extra curriculars, no socialization, mandatory social distancing, mandatory masks, mandatory health/temp checks every morning, no electives, no eating lunch together, no field trips, no dances/sports, increased time in "core four" classes. And furthermore, as outbreaks start occurring and forcing school closures you're at best going to have this start/stop thing happening all year long and at worst be forced to shut down again. Literally none of that sounds like a positive for mental health and well being, let along physical health and well being.