depends on how well fed, and how often they are fed i think. If they are starving, then will eat pretty much anything, if they don't need to eat (unlike a lot fish), they don't.
I'd imagine if a fry happened to sit very still in front of a cories mouth it would get eaten, but it's unlikely that they would actively go after fry when there are smaller, easier to get foods available.
They may not actually eat the fry, but we had four cories in with our Rams when they were spawning, and they stressed the rams ou to the point where the fry were eaten (not sure who ate them).