Get any milk or formula besides cow products. Cow products have fats and proteins that are hard for other animals with simpler digestive tracts to digest. Goat milk or goat kid milk replacer is digested well. Some use kitten milk replacer but while it's better than cow milk I prefer to try to stick with herbivorous milk or milk formulas. Soak the pellets in it until you get a firm mash, make it body temperature(warming up the liquid before mixing makes the pellets dissolve easier), and serve it on a lid or low dish. You may have to push a little in the rabbit's mouth at first. My 10-14 day olds have gotten the hang of eating that mixture and survived with no losses. Even older kits will have a better chance and won't need it warmed up as much. Very young bunnies are turned off by cold food. It's a challenge to keep it warm enough when you get orphans at the age they need handfeeding with straight milk. They'll stop sucking if it cools even a tiny bit below their ideal temp. Rabbits have a slightly higher body temp than we do so anything you feed young kits should be at least your temp, like checking a baby bottle on your wrist, but not hot enough to burn. You do have to clean them frequently especially the younger they are because once they get the idea they'll plow right in to the food and coat their face and chest.