When my oldest child was about 5 years old, she came down with a rash that appeared and disappeared. I took her to see the doctor; the nurse saw the rash, but by the time the doctor came in, it had disappeared. He told me it was Fifth disease. He told me it could take as long as 6 months for it to leave her system. Fortunately she was over it in about 2 weeks.

Fifth diseaset is fifth on the list of common childhood illnesses , with a rash, eg., measels, scarlet fever, etc.

I agree with these guys to always check it out if a possibility of Lyme.

 I suspect it might be as simple as a heat rash or allergic to detergent or more then ofen, fabric softener. Yes, it also could be  poison oak because it could be in the bedding etc. The oils of poison oak take two weeks to get rid of. The baby might be  reinffecting themselves by rubbing the oils in a different area where they sleep every night. 

Couple questions to help you:Where are the rashes located? Does it always come and go in the same spot or near the first outbreak? Does it come in certain times of day or after a meal?  Is the area exposed or covered by clothing?     

I agree with these guys to always check it out if a possibility of Lyme.

 I suspect it might be as simple as a heat rash or allergic to detergent or more then ofen, fabric softener. Yes, it also could be  poison oak because it could be in the bedding etc. The oils of poison oak take two weeks to get rid of. The baby might be  reinffecting themselves by rubbing the oils in a different area where they sleep every night. 

Couple questions to help you:Where are the rashes located? Does it always come and go in the same spot or near the first outbreak? Does it come in certain times of day or after a meal?  Is the area exposed or covered by clothing?     

A raised rash in a bullseye shape can be an indicator of Lyme, but in my experience is that it didn''t disappear and appear in other places.Recommend you see a doctor - you might want to have a look at Google Images to get a sense for what the rash could be: http://images.google.com/

Hey JoshD: I'm no doctor, but if this was my child I'd want to eliminate Lyme Disease. This is not my personal experience, but I've a friend who's child was diagnosed with lyme after spotting a bull's eye shaped rash that appeared to move. Personally, I'd go see a doctor, particularly if your child has spent time outdoors in a Lyme-prone region. Here's a picture from the CDC of a Lyme disease rash.  Here's a page on Lyme, specifically in children.