Sometimes! You definitely don't have to be a kid to have a theme party, but maybe you'll have to supersize a few items, because we're all Big Kids now. Either for your little one's celebration or picking up a few fun items for your own, Pottery Barn Kids has the most elaborate party collections I've seen yet:

County Fair party, Explorer party, Shipwreck pirate party, Water party a few things that I could get into...(seen here)
Explorer party tumblers
Hanging paper daisies
Jumbo inflatable bowling ball & pins
Ship centerpiece
Skee ball canvas game