Originally Posted by Zoe:
You did nothing wrong. As PP said, everyone is contagious before symptoms even start. You kept the dcp's informed and let them make their own choices.
My son started vomiting last Thursday. Nothing else accompanied it but I told the parents anyway. I kept DD home from school Friday because her throat hurt and I was convinced she was going to get the same thing as my son. She didn't, but ended up staying home another three days because she had strep!
Now my DH is showing signs. It's a long and drawn-out process to go through all family members and daycare families. But that's how it is. Thankfully all of my dcp's understood (most of them are in the medical field anyway and probably bring home more germs than their kiddos!
Don't worry about it. 
I had a neighbor boy (now 17) whose only symptom of strep was throwing up. He never had a sore throat. Wonder if your son is one of those types of kids.