My DD has just had hives too - she had a cold / sore throat and was really sleep deprived, and one afternoon just broke out in huge red spots, EVERYWHERE! She is three and this is the first time she has had anything like it. They were round and patchy, some looked like a red ring. They were itchy too. The Dr said they were hives and gave us zyrtec for her to take, which stopped the itching. They lasted for 3 days, and turned a purplish colour where she had scratched too much - it looked like she was bruised all over, poor little chicken. And then one day they just vanished! I hope they don't come back.... Dr said it is a reaction to a viral infection, almost like your body is allergic to having that virus.