I recently took my 2 1/2 year old to the er because he had a fever of 104.3 it's been 3 days now he has a rash all over his body almost looks like red little pimples along with a mild fever and diiharrea what could this be?

Roseola?: Roseola is a common childhood illness where young kids usually have 3 to 5 days of high fever, often over 104, which stops suddenly followed by a rash, sometimes with little red pimples that usually last for a day or two. The rash usually starts on the neck and trunk and spreads outwards to the arms and legs. It's usually not itchy. A little diarrhea with this is not unusual.

Viral rash: Although it is impossible to say for sure without actually looking at the rash, the sequence of events (fever, then rash) would suggest that this is a viral rash, such as roseola. If the temperature is coming down and your child is drinking and acting fairly normally, symptomatic treatment and observation are all that are needed. If worried--call your pediatrician!

Classic : This is a classic pediatric exanthem (rash) called "roseola infantum." this is usually caused by human herpes virus type vi or vii. It is self limited, common, and not serious. Your pediatrician can give you more details. See: http://kidshealth.Org/parent/infections/skin/roseola.Html.