What Causes Itchy Rashes All Over The Body Of A Toddler?

20 month old has rash. looks like pimples, doesn t appear to be itchy, baby is happy but is on elbow, diaper area, behind he knee, arms, legs, one pimple on upper and lower lip. think it could be chicken pocks but don t know. started small 3 days ago and continues to spread not fast but not slowly. I don t think I had chicken pox as a child and thought I would have by now if it was but don t know.