Niagra Falls is a world wonder and therefore a must see, but in my opinion you should see if from the Candian side. Go into the Skylon Tower for some food and enjoy a trip in the 'Maid of The Mist' for a first hand experience with the falls. In my opinion the falls are more impressive to kids around the age of 7-12, but regardless it is a must-have experience.
Niagara Falls: It's one of those bucket list items you've got to check off. Pack a rain coat and rain boots...you'll need them! After taking in this natural wonder, you won't look at buildings and roads the same way again!
Niagra Falls. I actually had a hotel room on the Canadian side that was just about eye level with the fireworks. It was fabulous!