Children's Riding Helmet: what size?

I want to purchase a safety helmet for my 6 yr old dtr. I found spirit troxel small at my local Atwoods, but I am not sure if it fits right. I tightened it and it seemed to fit well, but it still wiggles alittle on her head. Anyone have any suggestions on the right helmet size to buy?

If it's on and unbuckled she should be able to bend forward at the waist and not have it fall off. Does it come with those little pads? You can attach those along the sides maybe to get a snugger fit on the sides.

I had no luck with Troxel when I tried them on myself. They were really tight in the front and sloppy on the sides. My kids have them, but I need to recheck the fit.