What young rabbits can eat depends on what their parents were eating.
If they were not fed greens when they were with their mom you will want to proceed carefully. Feed only safe greens like parsley and cilantro at first and only a week bit. ANd only after they have been with you for at least a week.
IF they have been fed greens regularly while with their mom you should be just fine to have greens be a regular part of their diet...at first again, only safe greens like parsley or cilantro.
as your bunny matures you can give more or less greens as you desire. Be careful of the curciferous vegetables, they can cause some rabbits to bloat. I don't feed them since there are SO many options out there for feeding rabbits.
Carrot greens, parsley, dandelions, lettuces (particularly leaf lettuces), basil, oregano, various wild grasses/weeds (if you know what they are) plantain (the plant not the banana type thing), and such like. Strawberry hulls, raspberry and rose canes are good foods as well. Including apple and pear branches. DON"T do the branches of trees with nuts in them (aka peach or cherry)
Go very easy on things like apples, carrots, oranges, other fruits. Crackers, bread etc. Limited amounts.
Know that if you feed spinach and swiss chard they can turn the pee a reddish orange colour.
Pellets, hay are generally considered a good base for a diet.
Oatmeal, BOSS, wheat etc are also nice treats for rabbits.