Try a mouse, try frozen thawed, try live. Make sure that you little guy has enough room, 6 qt sounds awfully small for even a baby carpet as they tend to be arboreal during the younger years - saying that I used a 6qt to QT my IJ hatchlings when I first got them . . . hmm. . . .
Never the less, carpets are extremely picky as young snakes, and if they were use to mice, they will stick with mice, if they were use to baby cat fetus, they probably wouldn't touch anything else. You shouldn't worry quite so much yet, these guys go long periods without food, but definitely attempt mice when you can and see if that triggers it. If that was it, you're good to go.