The World Food Prize Hall of Laureates Garden is definitely worth visiting when you're in downtown Des Moines. The tulips are a little past peak now, but still quite beautiful. The garden features statues of Dr. Borlaug and John Ruan Sr.
My kids were kind of bored, but became a bit more interested when they spotted the name Norman Borlaug. They recognized his name from the book The Kid Who Changed the World, which is an excellent picture book for Iowa kids that also includes Henry Wallace and George Washington Carver.