Cracked corn is not going to "sink" into your soil, thingys will come along and digest it, however. If the birds have not discovered and devoured that cracked corn yet and if the soil bacteria have not stated to digest it yet you may need to do something more to stimulate the Soil Food Web sothey will digest it.

I just reseeded and put a thin layer of top soil/humus over the seed. I wonder if that will get the thingys started.

I have no idea what "top soil/humus" might be except something someone is selling to relieve you of your money. "Topsoil" is the top 4 inches of soil from someplace and it may or may not be anything worthwhile. Humus is the residual organic matter in your soil, the organic matter the Soil Food Web does not readily digest. even commercial compost needs to be looked at with skepticism today since people will sell anything they can.