S.S.
I second the cosi thing. We live in Oswego Ilinois but my son attends Camp Christopher each year for 2 weeks in the summer. on the way to or from we always spend a night in columbus and a day at cosi. Best side thing we have ever found on a trip. We went ahead a couple years ago and bought the family pass. it gets us into like 300 other museums (field museum , addler planaterium, art institute in chicago for example) its a completely hands on museum. your 3 year old will love it.
on a side note. you don't have to stay at those big water parks to go to them. we bought day passes for the one in sandusky one year. i took my youngest 2 sons to the waterpark for the day while my hubby took older 2 kids to the rollercoasters