We call that type a pan slab, as it would look like a pan if you turned it upside down. Sometimes you can get this kind of damage when the forms are removed from the foundation while it is still hot or green or to new. The usual trick is to glue it back on with white wood glue and pretend it didn't happen. That dosn't mean it couldn't be something more serious. On the up side if those are full brick over a wood wall, it would only be a few bricks sitting above the cracked area and the wood wall will be sitting on solid concrete. If you are north enough to get some freezing, water could be getting in there and freezing, making it open up.
I would clean out the loose stuff and smooth it over with a morter mix or stucco repair or something, just wet the area with a mixture of water and white wood glue just before you do it so it sticks good. And then keep an eye on it for changes.
Others here may have defferent ideas.