Transitioning from a KMR to Wet Food
Kittens should receive a proper and nutritious kitten milk replacement, aka KMR (preferably made of goat milk) until they are between 4 and 5 weeks of age. At this point, they can start to transition to wet food but don't expect them to just start eating it.
Feeding them the right food is important, but changing their food from infant food to fatty and nutritious wet food made for kittens (we use Royal Canin's Mother/Baby Cat cat food) is equally important. Whatever kitten food you go with, do NOT use one with fish. A kitten's body is not mature enough to remove any mercury that it might contain.
Transitioning needs to be done slowly, and watch the kitten's poop. If their stools start to appear loose or they are not going as much, increase the amount of KMR until resolved.
Generally, a kitten will not show any immediate interest because it's not the KMR they've been enjoying, and feeding time won't be as personal. Switching to regular foods will also shock their digestive tract, causing diarrhea or constipation. So, switching them over should take a little time.
Some will just stop feeding them the KMR because "...eventually they will start eating the wet food" (I've actually heard that). This is called Starvation, and it's not smart, and it's certainly not the right way of introducing them to wet food (in fact, that's actually quite dangerous, for reasons previously said as well as the potential that some kitten's bodies are not ready to be changed that quickly).
Here's how to avoid this frustrating dilemma: introduce the kitten to wet food by mixing a teeny bit in with their KMR (do NOT use a blender. That will add air, causing painful indigestion. Some call this "grewl."
Please note that you'll need to sacrifice at least one of the bottle/syringe nipples by cutting the tip down a little because wet food is thicker and chunkier.
As the amount of wet food mixed in increases, the nipple will need to be cut as well. This should be done little by little, matching the transitioning process so the increased chunks of the wet food can pass through without clogging the flow of food. However, if you cut it too far, too soon, the kitten could swallow it wrong and aspirate.
Every day, increase the amount of wet food you introduce to the kitten until it's too thick for the bottle or syringe. At that point, try offering it to them on a plate.
The resistant eater
If they are refusing to eat out of a bowl, try using a plate. If they're still resistant, here's what I suggest:
Start with the bottle/syringe feeding, then mid-way through, stop and dispense the rest into a large spoon and offer that to them.
After a few times doing that, they'll start lapping at the spoon. Eventually, you can start with the spoon and then, midway through, rest the spoon on a plate.
After a couple of times doing that, offer them the plate with the food.
Until they are eating off the plate, a little of the KMR should still be mixed with the food. Once you've achieved that, pat yourself on the back.
Celebrate [properly] because you've just walked the babies through one of the hardest times in their lives. Up to 40% don't make it.
Kibble, what kind and how much?
Introducing them to a proper sized kibble is important but simple; place about 1/8 cup of kibble per kitten in a bowl and place that down next to their source of fresh, clean water. That's it! We use Royal Canin's Mother/Baby Catkibble because it's made so small the kittens won't choke on it if swallowed whole.