MSD is correct: my rabbits get a diet based on free-choice alfalfa hay with some grass content, small amounts of whole grain (usually wheat) and as much fresh food (mainly weeds and certain tree branches) as the season will allow. They also have access to a trace mineral salt block, since they do not get pellets.
I'm sorry that my reply was confusing. If baby rabbits have full access to greens from the time they leave the nest, they will have not problems handling them. MSD is correct: they develop the proper gut flora during the nibbling stage, when their intake of solid foods is a small percentage of their diet, the rest being momma's milk.
Since you have not allowed this with the current litter, it is best to introduce the greens slowly. Dried clover, however, should be perfectly safe for any rabbits. It's really just clover hay!
I remember that I used to do what you do: hand feed momma her greens to keep the kits from getting them. Then a wise rabbit person explained to me that it is best to start off as I mean to continue. I've never looked back... and never lost a kit to greens in their diet.
Some very safe greens are the following: blackberry, raspberry and strawberry leaves and the lawn weeds plantain and shepherd's purse. These will not cause diarrhea and are in fact all excellent for treating it. See the
Safe Plants for Rabbits sticky for more ideas to cut your feed bills and let your rabbits enjoy nutritious, free greens.
safe-plants-for-rabbits-list-t55.html
Edited to add: While you can certainly feed romaine lettuce, carrots and cabbage to rabbits in moderation, I have found that the safest and best choices of greens are those found in the Safe Plants List. Best of all, they are generally plentiful and free.