You will love the Columbus Zoo. It's Jack Hanna's zoo and it is really well done. Zoombezi Bay is the waterpark there. I don't know that I'd try to do both in one day. The zoo by itself can be a full day. They just opened a new Africa exhibit and it's stunning. Between the zoo and Zoombezi Bay (just to the left after you go through the zoo's admission turnstiles) there is a little place called Jungle Jack's Landing. It has free shows throughout the day that are very educational, animal encounters (you get to pet lots of things like flamingos), and rides like bumper cars, a small roller coaster, a flume ride, etc. You can pay by the ride ($1 - $2 each) or get a wristband for unlimited rides.
http://www.colszoo.org/default.aspx
COSI can also be a full-day affair. We usually grab lunch in the cafeteria there. We love the 3-D movies and all of the hands-on exhibits. If you are interested in doing science experiments, go to the Gadget Cafe when you get there to sign up for a slot. They give you a menu of experiments and you decide what you want to do.
http://www.cosi.org/
Close to COSI is an area called the Scioto Mile. There is a nice big fountain to play in there.
http://www.sciotomile.com/
Easton is a great place to spend a morning, afternoon, or evening. Sometimes they have street performers there. (Great memories of a mime interacting with ds while we ate lunch outside the Cheesecake Factory.) There is a fountain area that kids can play in, the American Girls store, a
LEGO store, movie theatre, and many, many stores. It always reminds me of Disney just because there is music playing outside. They also have some special events:
http://www.eastontowncenter.com/events.aspx
Someone mentioned the Santa Maria downtown. That is closed until 2016 (doing some work along the river) and isn't wheelchair accessible anyway.
http://www.santamaria.org/
The Franklin Park Conservatory is a really lovely place to go.
http://www.fpconservatory.org/
The Firehouse Museum is good for a couple of hours.
http://www.centralohiofiremuseum.com/
And the main branch of the Columbus Metropolitan library is downtown. We love to hang out there. And it looks like most afternoons this summer from 2 - 3 they have a kids' activity. For example, on there is a balloon workshop where children learn to make balloon sculptures. There's also a really nice children's area to play in.
http://www.columbuslibrary.org/
There are lots of beautiful metroparks with playgrounds, trails (many of them paved), and programs. Inniswood Metro Gardens in Westerville is particularly lovely and has a charming children's garden (called the Sisters' Garden). (Inniswood has a turtle program next Tuesday and Wednesday at 10:00 and 1:00 each day.)
http://www.metroparks.net/ParksInniswood.aspx
Main metroparks site:
http://www.metroparks.net/
The Columbus Clippers have away games next Mon-Thurs. If you're there Sunday or Friday night that might be an option. The ballpark is beautiful and very close to the Convention Center.
http://www.milb.com/index.jsp?sid=t445
There is a Columbus Crew games on Wednesday:
http://www.thecrew.com/schedule
This looks like fun:
http://www.experiencecolumbus.com/e...se-Man-and-Other-Fairly-Stupid-Tales/id/42319
The Ohio State Fair opens next Wednesday! The fairgrounds are just up I-71 from downtown.
http://www.ohiostatefair.com/index.php/general-info-34
I agree that the North Market is very nice and a great place to eat.
http://www.northmarket.com/
And Bucca di Beppo
http://www.bucadibeppo.com/
I've not been but I've heard good things about Dirty Frank's Hot Dogs.
http://www.dirtyfrankscolumbus.com/
Max and Erma's started in Columbus. There's one in the Arena District.
http://www.maxandermas.com/