Decoration Day is another possibility.

I used to live a few miles from the Chickamauga Battlefield and on Missionary Ridge. I've explored most of each battle site and wonder if this gentleman was a member of one of the 40 regiments of Ohio volunteers who fought there. If so, he certainly had stories he could tell.

During the 19th century little boys were often dressed in outfits like this. Personally, I don't understand it, but there it is.

As Aenthal noted, this appears to be a Union civil war vet wearing a GAR medallion and an Ohio uniform of some sort. I've attached a photo of a fairly similar badge with flag, eagle, etc.,from the 181st Ohio Volunteers. It's hard to tell, but this looks to be what our featured gentleman is wearing!

The pin on his "uniform" jacket appears to be a GAR medallion. GAR is the Grand Army of the Republic, a veteran group for former Union soldiers. That it says Ohio is consistent with being a GAR badge. The chapters were geographically organized. GAR did things like hold camp out reunions and trade ribbons/pins buttons at least once a year, for many years after the Civil War. Think grown up super boy scouts. They also held fraternal gatherings locally and had considerable political clout. It is said one could not be elected to the presidency without the backing of the GAR. The flag and uniform suggest that he may have brought this daughter (grand daughter?) with him to some GAR gathering (which might be something like a lunch after participation in a 4th of July parade). That would make this photo date from the 1880's, possibly 1890's.