Until I know for sure what it is I would not risk my children, husband, the other daycare children or my own health I wuld not have him in care. What you don't know can KILL you when it comes down to unknown disease. I have a policy that stats:
Doctor's Notes
I hold the right to ask for a Doctor's Note before your child can return to care.
I also have the right to refuse a Doctor's Note, if I feel that your child is not ready to join in all activates or just isn't ready to return to care.
Sending your Child Home
I hold the right to send your child home upon arrival or during the day if at anytime I feel that your can not join in all activates, is uncomfortable, or any other reason I feel is justified.
this way if I am not comfortable with the medical problem, then I don't have to deal with it. I am not a Dr. or a nurse.

if it is just a reaction then as long as the child can join in all activates I would let them come, but for something that is unknown I personally would not be comfortable.