Holy moly
Are you new to daycare? Just asking because it's going to take some effort on your part to develop that backbone that tells you 'this is not right and does NOT belong in daycare'. Safety and health for you, your own family and the rest of the dcks comes first and foremost when you have a dc. I accepted way too much back in the day, always 2nd guessing myself and thinking it was all me; we're talking 38 yrs. ago. We had no support systems to speak of, not to mention any place like daycare.com to lean on for advice and support. Confrontation(for me) has always been the hardest thing to deal with, whether it was asking for payment, talking about their child's health or behavior, etc. It's not easy but one of the most important things you need to be able to do.
Do you have a contract and handbook of policies? If not, create one ASAP and issues such as yours would be clearly spelled out. If you need to create a contract I'm sure a lot of people here could advise or contact your state's childcare site; you can even search online. I don't know if you're licensed but you still need policies to enforce. And never back down because you lose all credibility.
I spent too many years being nice and wanting to help; it only comes back to bite you in the butt. And when it comes to health, now is NOT the time to take risks.
Just one more thing I got from your post. Guilt. You need to lose the guilt because it'll do a lot more harm than good in this biz.
Good luck. And I agree about not allowing them back, even today. They'd be gone.