As I mentioned, we have one (cottontail). They're EVERYWHERE around here. The mothers feed them at night, and yes, when they move from milk to solid food it is the bunny berries that the kits eat first. Rabbits have a two pass digestive system. The first pass breaks down the fibers and the second allows them to take in the nutrients.
My wife has pictures in her camera (haven't uploaded them yet) of a kit we had out a week ago. The neighbor's cat (same one that shits in my garden) is proficient at rabbit hunting. It got all of the kits but one from a warren in my next door neighbor's yard. I took it out and held it for a while as they were digging a hole ten feet away and transferring the fur from the first to the second. It was tiny and obviously still nursing. I'll recognize it - there was a white stripe on it's forehead. I really hope it made it. And touching them does NOT make the mother abandon them. That's a myth.
If the kit is old enough to eat solid food, you can take it in and feed it. Don't give it much spinach (too much iron), but kale and any greens but iceburg lettuce are good. They also need timothy hay. Even though most "pellets" are made of timothy hay you still need to give them the real deal once in a while. And the "they don't need water" thing is bullshit. They drink from a bowl and they self potty train. Once you take it in, you can't let it back out. It's a domestic pet at that point but they make excellent pets. Just arm yourself with a lot of Neosporin. You will get scratched. I've never been bitten by one but they all kick.