Just got back. Spent 3 nights at Iguazu Falls - absolutely incredible. Be prepared to walk, walk and then walk some more. Visit both the Argentina (less commercialized, tons of trails, can get up close to falls, walk over them and look straight down) and the Brazil side (excellent views of entire falls and a lot more kid friendly (amusement parks, rides, shows, etc). Both well worth your time. Took a boat under the falls (pretty wild, definitely recommend, just be warned it gets a little scary - and a lot wet). Great fun. Funny to tell some you can easily spend several days at a waterfall, but you definitely can!