You've somehow got to scrape some money together and get that little one to a vet. People are more prone to adopt a kitten than a full grown cat, even if the kitten is sick or injured. (In my case, that's the only kind I have adopted.) Yes, they're eating what Mama kills but they'll probably get fleas and tape worm as a result. And cats need the amino acid taurine in their food or their eyesight is in jeopardy, possibly even resulting in blindness. I know it's an inconvenience but PLEASE get that little one to a vet. It's still early in its life and the vet can probably do some simple, inexpensive treatment that can save its life. PLEASE ACT NOW!