My daughter caught this a number of years ago, when she was 5 or there around (she is now 11). She had 2 bouts of it within a year & half of each other.
At the time, I did everything you are doing now to understand what it was and how to treat it. I came across a treatment that worked so well that I bought extra vials of it to have on hand should it come back again in the future, as it does.
I am want to tell you, I have NO affiliation with the product or whoever produces it. I just can tell you that it really worked for us, both times she had the bumps from this virus. Also, both times she only had the bumps on her trunk (stomach & back). And from what I read about others with the virus, it seems that her case would have been considered fairly mild. But it was a problem for her as the bumps itched and hurt her.
All that said, the product we used, and which I still keep a vial of "just in case" is called "ZymaDerm" or "ZymaDerm 1". I bought it off of Amazon, because I trust Amazon and knew if it didn't work I could either return it or make a post about if it worked or not on the website. It comes in a vial with a "rod" inside attached to the lid. All you do is use the rod to dab some of the oil-like substance to each bump twice a day.
It is made by a company called "Naturopathix, Inc. I recall it wasn't what I would consider cheap. Another reason I was hesitant. But in the end, I can only give you my word that it worked, and worked well for us.
I am not one to make posts on sites like this, I am more of a reader than a commenter. But when I saw the title of your post, I knew I had to respond with a post. I remember the horrible feeling I had a the time not knowing what to do to help my daughter. And I was scared she would suffer for a long time since there didn't seem to be any real treatment that would work 100%.
I hope you will look into the product for yourself and if you find it is something you decide to use, I hope that you get the same good results that we did.
By the way, I am sure this has nothing to do with the product we used, but she has not had another bout with this since, fingers crossed it stays that way. Just a bit of hope to let you know that it doesn't seem to be a huge problem that you have to continue dealing with for years.
Good luck!