I really, really feel for you all. It's a decision I would hate to have to make, but like many of you, I'd be feeling as if I was being backed into a corner to make a decision I really didn't want to make, either way.
I really don't see how it's going to work at all. Could/would children wear the see through masks? I really don't know at all. Like Louby said, how can we be expected to care for strangers children, whose backstory for isolation we don't know, and not be able to see our own grandchildren? Definitely not be able to see them once preschools are opened up and the potential for viral risk is increased.
Could parents remain briefly whilst a child's temperature is taken, on arrival, and take the child away again if temp is up? (The problem with that is that resting temps can vary considerably. As a child, my resting temp was only 34.5, that was my normal. I had convulsions a couple of times when it went just above 37.5, and my 'normal' was written it big red capitals on my notes after that. So a child could present with a temp of 37 and be deemed okay, when in fact, that's really high for them (if you catch my drift).).
Big hugs to all of you - I really hope your Counties come up trumps and give you some solid support, or at least take the decision, blame and consequences out of your hands.