A couple of comments. I note that few of the comments consider the teachers and other school staff - all of whom may live with families of their own and would, therefore, be putting them at risk. Many teachers live at quite a distance from their schools and will have to travel, possibly on public transport.
It is also the case that at the current time the effect of the virus on young children is not understood and children could be showing no signs, whilst being a carrier.
I cannot see how in most schools distancing can be observed. Even in primary schools where children may spend most of the day in the same classroom, they will still probably need to get to their classroom by way of a narrow corridor - although some school building will allow that to be avoided. They will need to be using the toilets.
How much of the discussion around opening schools is about financial impacts, rather than lives.