Most recent data I could find was 2008 when 16 cases of rubella were reported.
I think with something like rubella, getting an accurate number of true cases in children might be difficult since often the symptoms are so mild they go unnoticed or they are thought to be something else.
they are basically runny nose, mild fever, swollen lymph nodes and a red blotchy rash. How many other viral illneses present this way? Older people, especially women, often get joint pain as well.