dilemma

I don't know how to even go about explaining what happened today. I picked my kids up early and took them to the place we usually go to so they can play for an hour or so before dinner. One of the parents I know, it's not like we're tight (I'm not really tight with anyone) but we talk when we're up there, wound up backing into my car. I saw the whole thing from a distance of about 50 yards. The parent got out of there car, looked at my car and then got back in their car and drove off. Now it's not like my car sustained major damage, hardly, the paint got scraped where my bumper was tapped. It wouldn't be a big deal if this parent had bothered to walk over and say something to me. But they didn't. I don't know why I didn't get up, maybe I assumed they would come over to me? I honestly can't say. But it makes me feel so crappy. And I don't even know what to say to this person next time I see them. Thanks for the hit and run on my car? I avoid conflict like the plague, so I'm obviously not going to say that, but what would be a way to politely get the point across that it totally wasn't cool to back into my car and then drive off hoping that I didn't see what I did?