I don't remember chicken pox parties, but I remember my 3-year-old cousin came home with it one day and we were encouraged to play with him, not that it was much fun playing with a cranky, itchy, crying toddler, even though he was nowhere near as ill as I was when I finally caught it.
A few days later, my 7-year-old brother caught it and I was encouraged to play with him, too, although I was at school most of the day, my mom was at work, and my brother was at my grandma's house. So by the time my mom collected my brother from my grandma's and me from school, I had too much homework (as a fifth-grader) and he was feeling too under the weather to play. It took me a couple more weeks, until about early February, to get it- I was ten, and since I was a little older than my brother and my cousin, I was ridiculously sick. I didn't get sores on the inside of my mouth, thank goodness, but I was covered in sores - especially my scalp - ouch. I couldn't even wash my hair, I was in such pain.
I wish they'd thought to expose me to someone else with the chicken pox when I was younger, so I could have gotten it over with earlier. The week(s) I was off school was one of the weeks our school spelling bee took place, and I had been our class winner.

I had to miss the spelling bee, though, and I was devastated. Plus, that year brought some of the worst late-season storms and flooding in my lifetime, so I was trapped inside in miserable weather, sick and bored. Thank goodness I was also sent to stay at my grandma's, but I was so weak and sick that I begged my mom to let me stay at my grandma's house that whole two-week period (I say my grandma's, but we were just used to calling it that - both my grandparents on my mom's side are still alive). My mom would come over in the evenings and give me an oatmeal bath and a calamine rub and soothe me before she went back home every night for the whole two weeks I was sick.
That year brought some of the worst late-winter storm weather EVER to Northern CA, too, so I was glad I didn't have to go to school in that, even if I was pretty miserable. We didn't get a majority of the flooding and etc, but it was constant rain for the whole two weeks I was sick. I think my grandparents' basement flooded; I forget if it was that time or another time. It was torture - being sick, weak, itchy and being told not to scratch - but being with my grandparents was fun because I was grandpa's little girl (and still am) so I got all the treats I wanted (candy, ice cream, books and games to pass the time, etc), and my grandpa did everything he could to comfort me once my mom went home. It was a big help to my low spirits. He hated to see his little girl sick and suffering.
To this day, whenever I'm under the weather and my grandpa is here at my house, I will go and snuggle up with him because the reassurance always helps. Of course, I don't do this when I'm actually SICK, just when I'm not feeling emotionally well, because he's 81 now and in frailer health than when I was 10.
Still...I've never been to a chicken pox party. I don't think they're all that common now that there's a vaccine for the chicken pox, are they?