Like said above, if they're abnormally this or you're conditioning them for breeding, heavy feeding with large large water changes is great (beef heart). But if not, then fit, lean (not thin or skinny) fish are healthier. The best foods for a normal diet are probably Omega One's shrimp pellets. Made just for cories.
People typically can condition Corydoras to spawn by feeding them high protein foods, which Bloodworms can work. It may take up to 2 weeks of feeding. You can also trigger spawning with large water changes will cooler water (mentioned up to 10*F cooler water, but I wouldn't go that cold.
Another trick along with that is when doing the water change, leave the water level low for a while (I mean low, maybe just 3-5 inches of water depth, you can save the tank water in a bucket if you wish to re-add it rather than use all new freshwater). The low water level also can trigger spawning behavior in the corys.
There is also methods using natural hormonal methods, but those are more advanced and can be tricky.
Other than that, just the corys being happy in their environment is the best thing. If they are very happy with their lives, they will breed with no need to do anything special, not even conditioning with protein packed foods or cooler water changes. Larger groups can have them feel happier (yes, just a pair can breed, but large groups does make them happier, just as they are in nature).
But yeah, if they are too young, not matter what you do, they won't breed haha.
Shrimp pellet's as mentioned,and New life spectrum pellet for small fish are good staple diet .
Blood worm's, meh. Mostly moisture by content, and have been associated with health issues(internal parasites), not too hard to imagine considering where they come from and possible freeze/thaw during shipping.
Much better nutritious food's to be found.
Fishes do love the blood worm's though.