No Notice of HFM Outbreak During Week my Son Didn't Attend School

So I returned to work after maternity leave last week. After an unfortunate incident last year where my son caught COVID two days before Christmas (thus ruining Christmas) my policy now is to pull him out of school for a week before any major holidays. I did that the week of Thanksgiving. He normally attends 2 days per week. When I picked him up yesterday, I was behind a dad talking with his teacher about "oh yeah, she's getting better now" referring to his daughter. The teacher was then talking about how the entire toddler class "got it last week." They kept talking about it and I finally asked "what did the whole toddler class have last week?" She goes oh, hand foot and mouth, you didn't know? No I didn't. There was no announcement made and despite my son attending both M and W last week, no one told me. The teacher seemed uncomfortable because while I was polite, it was pretty clear I wasn't happy we weren't notified. Had they told me, I would never have sent my son this week, since HFM is contagious for quite awhile. I ended up messaging the director to express that I was pretty frustrated no announcement was made, because I would have made different decisions about attendance last week if I had known, especially since we have a tiny baby at home. She told me the whole toddler class got it last week and now seem "over it," so she didn't think they needed to inform me. However, some of these kids are returning after only 1 day fever free, with obvious lesions. They are clearly still contagious, and my son was definitely exposed all week. This is not the first time multiple kids have been sick with something and no announcement has been made. Is this normal? Am I wrong to be as frustrated/angry as I am that I wasn't informed until after I had sent my son for a week around kids recovering from HFM?