If I was a travel insurer, I'd carve them out. I think you are right re: entry/exit - and I assume a covid test prior to travel will be required for everyone, including children. This is why I wouldn't insure them if I was running a travel ins company (something I know nothing about so take this with a grain of salt)- if a 6 year old tests positive, and thus cannot return home until not positive, think about all the expenses associated with such a change of plans that would have to be covered. No way will an insurer take on something that has such a high probability of happening relative to other things.