I had a 1950's Bowling party for my daughter who turned 6. It was at a local bowling alley. Besides all the guests coming dressed up complete with slicked back hair (boys) and poodle skirts (girls) we drank Coke out of old fashioned bottles and the goody bags consisted of candy that was popular in the 50's. These were gotten from a website called nostalgiccandy.com.  The cake was a big greay poodle.  If the kids were older, I would have done root beer floats with the lunch but I didn't think 6 year olds would like that flavor.