If you're in Columbus looking for a nice place for your children to play, I would definately recommend Friendship Park. This great space is located in Gahanna, and most people probably don't even know it's there. It's spacious, very green, and has a newly re-done play area for the kids. There are also covered picnic areas, and last time I was there, they had a vegetable patch!
The playground offers a climbing wall, several slides, things to jump on, tubes that sound travels through (talk in one side, and have your friend listen way on the other end), and something else that's cool. An area for much smaller children, as well!
Friendship park also hosts a slew of musical events throughout the year, such as "Summer Music in the Park".
I definately suggest checking it out!