My nephew is only 3 years old and has the chicken pox. how many days will it take for them to go away?

Perhaps a week: In most cases it takes upwards of a week before all the lesion's have crusted over. This is when one is generally no longer considered to be contagious. Sometimes it can take longer if there are a lot of lesions, shorter if there are only a few lesions.

Varies: They are considered contagious from the day before the rash started until the last one has scabbed & dried or a week later, whichever is longer. The healing depends somewhat on the kids scratching and any additional problems that can cause. most fade initially within 3 weeks but skin changes can last a year.