Are the Niagara Falls the highest falls in the world?
No.
Niagara Falls is known for the beauty of the huge naturally shaped Horseshoe Falls on the Canadian side. The Niagara Falls are 57 metres tall or 187 feet high. It's the volume of water falling over the crest of the falls that's also magnificent and thunderous because it's 681,750 gallons of water/second. Yes, per second. Remember, you can stand so close to The Falls that you'll actually get wet so it's an overall amazing experience.
The tallest known waterfall in the world is in Venezuela at 979 metres or 3212 feet.