Not punishing them at all. Just fact of life. This was the last realistic opportunity for a visit before the Easter Holidays.
Long term, it's very simple, they are not reliable enough for "childcare" and anyway it is clearly too much of an imposition, therefore there will be no "passing through" visits by me in future because I will not be passing through on the way to events, because I will not be doing those events unless DH is not working that weekend. The weekends they "could" see the kids have reduced by 25% as a direct result as DH needs not to be working (he works 1 in 4 weekends).
I will not stop DH planning family visits to them when they emerge. Nor will I prevent them from visiting us. All that will change will be opportunities (much requested up to this point) to have the kids to themselves will not arise as a result of my plans, because I will not be making plans.
We have 3 weekends before we move - which will be rather busy with packing stuff.
After we've moved the journey time becomes difficult for a weekend away with DC, especially if we have to wait for DH to finish work... We therefore need a school holiday- which at best will be summer half term or the summer holidays.
Or of course school closures would give an opportunity, but that would hardly be a responsible choice.
Neither have pre existing respiratory issues, so seeing DC now, when there are few fewer cases, most of which are linked to Iran, Italy and the Far East, circulating than there will be before the summer would seem to be less of a risk than seeing us later in the year.
They are allowed to make their choice, I will simply point out their lack of logic if they do change their minds at the height of the outbreak, and leave visit facilitation duties to my DH...