This is a strep throat infection with a rash.
The rash is caused by a special rash-producing toxin that is present in some strep bacteria. The rash usually appears 18-24 hours after developing a sore throat and a fever. The skin appears sunburned, with very small red bumps and it feels rough, like sandpaper. The rash usually clears in 4-5 days after treatment with penicillin. Occasionally the skin will peel where the rash was most prominent.
Your child is no longer contagious after being on the antibiotic for 24 hours. The rash itself is not contagious.