I have fostered for PetsMart, but I never attended any adoption days. I don't know who adopted 'my' kitties, but I am certain the PetsMart adoption associates found them good homes. I prefer to not know about them, this way I can imagine them always happy and loved.
I also would bring a sheet of paper for each kitten, like a flier, with their name, a picture of them in the corner and describe how they liked to play, with what toys and list their litterbox and scratchpost habits and food preferences. I also would have baby-photos printed up and in an envelope stapled to each kitten's flier, so their new owners could have some of their baby pictures.
You are doing, and have done, a wonderful thing for these babies by fostering them. You have given them the best possible start in life and a chance at happiness because of the PetCo adoption process and policies. It is hard to let them go, I know I have trouble, but I figure I get them when they are cutest. ...and fostering satisfies my kitten-lust without angering my resident housecats with more permanant additions.
You've done good!