Good on you for taking the baby in and even more for your willingness to get help. We had a crash course in neonatal kitten care ourselves. It’s scary how fast they can crash and you have no idea how long this one’s been without proper milk already.
BTW, definitely don’t give cow’s milk. It’s not only not helpful, it’s actually harmful. Kitten milk replacer is the only thing you can do right now. And these babies have to eat many times a day.