Can someone diagnosed with juvenile rheumatoid arthritis grow out of it?

No, not at all. There is no way to "outgrow" jra / jia. It can only be put into remission for periods of time from weeks to years, depending on what type of juvenile arthritis it is and how many joints were involved at the time of diagnosis. Kids with more active joints at diagnosis are more likely to flare more often when off meds. Until a cure is found, we work for remission with minimal flares of diease.
Possibly. There are several forms of juvenile idiopathic arthritis (jia, formerly known as jra). Some forms are self-limited and the child will "grow out of it" during childhood. Other types of jia are more severe and can cause permanent deformities. Now that there are treatments for all types of jia, it is more important than ever to have an accurate diagnosis and treatment by a rheumatologist.
It depends. Jra means you have a chronic disease that includes arthritis as one of it´s components of a cause that is not known. It is important to get tretment early once diagnosis is made and to be very familiar with the different types of the disease as they have different outcomes as well as demographics. Many kids, depending on the form of jra may grow out of it with proper treatment and close follow up.