Final answer:
Roseola is the common illness in young children that starts with cold-like symptoms and leads to a rash, mostly due to HHV-6. It is similar to fifth disease in presenting cold-like symptoms and a rash but differs in rash location starting on the torso compared to the facial "slapped cheek" rash in fifth disease.
Step-by-step explanation:
The common illness in young children often caused by a mild infection or as a reaction to a new food or medication is roseola. Roseola, also known as roseola infantum or exanthem subitum, is a mild viral infection that is most commonly due to human herpesvirus-6 (HHV-6) and occasionally by HHV-7.
Similarities between roseola and fifth disease include that both are viral diseases that begin with symptoms like a cold, a fever, and lead to a rash. However, a difference is that roseola typically causes a rash that starts on the torso and might spread outward, whereas fifth disease is characterized by a "slapped cheek" facial rash before spreading to other areas.