The Maid of the Mist and the Butterfly Conservatory are the things that come to mind that you and the 3 year old would enjoy.

The Niagara parks commission runs a demonstration garden downriver that is charming. Nearby is the cable car crossing the gorge above the whirlpool rapids. Also along the way is a statue of General Brock atop a tower overlooking the river. Brock led the defence of Queenston Heights in the War of 1812 and was killed in battle. Not long after the memorial was erected, naughty Fenians blew it down so you will see Brock II and a nice park. Carry on to the mouth of the river and Niagara-on-the-Lake, a chi-chi summer retreat a century ago and now home to a major drama festival in the summer. Also open for military displays in summer is Fort George, a wood-picket fort that lobbed cannon balls at Fort Niagara during the sad war. And all around the town are wineries as it is the heart of eastern Canada's wine region.
I.E.: Admire the Falls, then avoid the tacky Believe-It-Or-Not tourist hucksters by getting out of the city.

If your time is limited, I would spend the time admiring the falls. Start where the falls actually flow over into the river. It's a great spot for pictures .
Then walk all along the railing until you are in front of the American falls . Children seem to enjoy walking along by the railing
If you have time, go on the Maid of the Mist perhaps go there first to get your tickets .
Buy a ticket for the people mover,,and ride it along, hopping off different places to see the view .

Drive down the Niagara Parkway to Niagara on the Lake and wander down the Main Street.

Enjoy your time in Niagara .

There are two distinct municipalities.

The City of Niagara Falls is where the falls are, and you can get within five feet of them. The kid should enjoy the Maid of the Mist, and so will adults. ($20 each for adults, and the kid is free)

Bring plastic bags and rubber bands for your camera.

The Maid fo the Mist is the single best tourist attraction in the entire world, incidentally.

Someone's already suggested the buttrfly conservatory. Close focus lens -- eal macro is even better -- plus a three year old makes a good combo.

Second municipality os Town of Niagara on the Lake, with a fudge store and an old fort with lots of running room, both attractive to three year olds.

Welland Canal has big freighters pasing through. Photographers like this; kids usually do too, but three is pretty young.

If you are working on this trip, tell me about the assignment and I can get way more specific on photo subjects.

The total area is one of the nicest place of the world you may enjoy, though you have a limited time you can take the choice for The Maid fo the Mist, the water falling point or Welland Canal

Just following-up on BAK's post re. the Welland Canal. Catching a ship at the Lock 3 Visitor Centre in Welland can be kind of hit-or-miss. During the shipping season, the following link can help you narrow the window down some.

http://www.greatlakes-seaway.com/R2/jsp/R2.jsp

Also, if you stop by they usually have the ETA for individual ships written on a board by the information desk. Best lighting for an up-bound ship during the summer would be sometime from about 6pm to dusk.

BTW, when you say "limited time" how much time are you expecting to have?

u

utrechtman, Only you know what your must-do things are. Here is a list to help:

THINGS TO SEE AND DO IN NIAGARA FALLS AND REGION:
Maid of the Mist
Journey Behind the Falls
Niagara's Fury
White Water Walk
Whirlpool Aerocar
Botanical Gardens
Butterfly Conservatory
Floral Showhouse
Bird Kingdom
Whirlpool Jetboats
Skylon Tower
Skywheel
Imax Theatre
Indoor Skydiving
Clifton Hill attractions - Tussauds, Ripleys, Guinness, etc.
Marineland
Safari Niagara
Fort George and Fort Erie
Dozens of wineries
hiking in the Niagara gorge or Bruce Trail
Shaw Festival Theatres
Welland Canal
Fallsview Casino and Casino Niagara
dinner theatres
Over 30 golf courses

http://www.niagarafallstourism.com/
http://www.niagaraparks.com/
http://www.cliftonhill.com/
http://www.fallsviewboulevard.com/
http://www.niagaraonthelake.com/page/Featured_Events
http://www.tourismniagara.com/

Thanks all. And a special thanks falls dude and south am!

The OP has only 1 night. He needs some help with priorities.

Seeing the falls is a given. The Maid of the Mist takes perhaps 1 hour total. After that, what?

With limited time, I would drive downstream along the Niagara Gorge and visit the Butterfly conservatory AND the adjacent Botanical Gardens, which are stunning and full of photographic subjects.

If I had time to spare, I would visit EITHER Fort Niagara on the US side OR Niagara on the Lake, which I assume will be full of war of 1812 events this summer. (Aren't there people costumed as US occupying troops on the main downtown streets?)