If you breathe oxygen, it's on your bucket list. Heck, there are probably even some alien life forms out there that want to take their kids to Niagara Falls. It would be hard to overstate the breathtaking power and natural beauty of this international landmark, the first of our national parks, but I'll do my best.
I was lucky enough to stumble, with a little good advice, onto an itinerary as easy as a vacation should be, allowing our family to see Niagara Falls from above and below, from in front and behind, by day and by night, from the US and from Canada without waiting more than a few minutes in any line or spending a lot of money. To be fair, we pulled off this feat in June; repeating our movements in July or August might be more crowded, but I still think it will be the path of least resistance. Or you could go to the other extreme and see the Falls in winter, which by all accounts is a whole other kind of magical.
If you have time to explore a few fun things beyond the waterfalls—of which there are overwhelmingly many—there are some great free options. You'll run out of time before you run out of things to do in Niagara.