Oh God, I know this is pathetic - but I need reassurance

[twoisenoughmum]

... my DCs spent an afternoon last Wednesday with their little friends, one of whom had been sick the night before (Tuesday), the other was sick on the Wednesday night. If they were going to catch the bug, would they have done so by now?

think so, usually it takes a couple of days at the most.

Yes they would have caught it by now.

I would have thought they would have it by now if they were going to. I hope they avoid it for all your sakes.