I've seen this before. I think your "pups" are actually small members of some sort of cow nosed ray and the big ones are of course our beloved southern sting ray. If you look closely I think you will find that the small ones are more diamond shaped. I think they come in close to shore in the surf like that to feed. Most rays eat shellfish and other inverts and I know we have plentiful coquina clams and "sand fleas" on our beaches. I have noticed that the small rays spend more time zooming around in the water column in a kamikaze-ish manner so they may, perhaps, be feeding on something in midwater, but don't quote me on that.
