What is it?

Having a long week already. Frannie ended up with some strange hives yesterday. Anyone out there have any guesses? She went to school yesterday morning with no bumps and when I picked her up at 3:00 she had little red bumps from her neck to her toes. Mostly on her belly. Nothing unusual to eat at school or in the morning at home. No new detergent at home or soap. This am she is better, but I gave her some Benedryl anyway. Grace and Frannie are both coughing some, but they are on their way to school.