Pink eye comes and goes so often I wouldnt' worry too much about it. Now that you know be extra vigilent about hand washing for everyone and especially yourself as you move from child to child. It is spread by direct contact so limit if you can access to the eyes - a good day to play games together that keep the kids busy but far enough apart like dancing to music. Yes the ill child should go home till he can start meds.

Think about what the child has done since he got to your house and try to set aside any toys he touched so they can be washed.

I take a relaxed approach to most illnesses in the sense of the stuff is out there and goes through any group no matter where you are. It isn't even safe walking through the mall or riding on a bus. The ill child goes home and to the doctor for confirmation and advice. 48 hours on meds and they can usually come back provided eyes have stopped leaking but watch the other eye since it often travels back and forth. When you know what it is for sure then mention to the other parents that one of the kids has it and letting the parents know what to look for in their own kids and then just carry on with fingers crossed.

If you want to be prepared for your own family you can buy drops at the drug store = polysporin makes one that is good for eyes and ears and is great to have on hand for use at the first sign of infection. Then if that doesn't stop it you will need to do the doctor for something stronger.