Unfortunately, many of those staff who are overseeing what is going on in schools are key members of staff, simply because of the specific requirements in terms of not only staffing but also who is trained in what, including medical issues as well as everything else.
When a school is open they have to have certain trained staff members on site. Until there is some type of cure and/or vaccine schools simply cannot guarantee they will have the correct staff.
And not all staff want the extra responsibility of knowing CPR, about seizures, how to use defibrillators etc. So quite often schools may only have two trained staff. If one of them is off ill, the school have to then assess if they can still safely meet the needs of that individual student. It's not an easy or ideal choice to make. And it is no-one fault at all, and nor should they be criticised for it.
Sometimes what parents forget, and not aimed at anyone, is they only look at their own children's needs, which of course nothing wrong with it. So they understandably don't see the issues faced on a daily basis. Children that sit and can concentrate, and want to be there, and stay engaged aren't consistent across the system.
There are so many children needing support that quite honestly staff shouldn't be forced to do. And quite often it can and does boil down to this. Peer pressure from colleagues can be harsh, even worse when management join in.
They are expected to be - mum, dad, father figure, mother figure, teacher, social worker, therapist, nurse, and much much more. That can be the expectations btw of some Ta's who are also expected to work beyond their paid hours.
To you, your teachers will always be friendly and nice about them still working. Technically even though I no longer work there I cannot mention the school's name. We have to be positive even when there's an explosion in the background. However, behind the scenes, there is a possibility that one of those teachers explaining the negatives is staff from your own child's school, even the childless ones.