My 2 year old has a rash on top of arms and around her genitals. What is it?

Contact dermatitis. Strange distribution....I would like a description but most common scenario would be that the toddler was reacting to something that contacted both sites, such as poison ivy in the woods in summertime. Secondly, perhaps new topical cream was used by mother, however moms don't usually use the same cream for diaper area and body.