Kids get sick SO often in those first years. It probably has almost nothing to do with who has what that comes around them. They get sick. ALL the time. If it weren't one kind of sick, it'd be another.
And I was the mama-bear germ patroller extraordinaire when I had DS, but I've had to relax. And I've seen all of DS's friends be sick all the time, too. That's just how it goes.
In less than 12 months DD has been sick CONSTANTLY. And her white cell count is off per her PED. I just asked they not come while they were sick with mono. It was the last thing we needed to catch and it is really contagious. I wasn't trying to be an "evil step mom". I love those kids.
Yes they got their feelings hurt. And yes I was trying to protect my DD from another round of sickness. I never meant to make them feel unwelcome. I just didn't want DSS to come over while running a 103 fever. When he was that sick is when I asked DH to have them stay home rather than visit that weekend. I figured by the time our next visitation came up (two weeks later) he would be feeling better.