What can a 3-month old rabbit eat?
More fresh leafy greens that rabbits can eat: cucumber leaves, mache, red or green leaf lettuce, romaine lettuce, spring greens, chicory, fennel tops, borage leaves, dill, blackberry leaves and stems, strawberry leaves, sage, lemon balm, marjoram, savory, Russian comfrey, boston lettuce, lovage, oregano, thyme, cilantro, chervil, tarragon; wild plants: plantain, thistle, chickweed, bramble leaves, shepherd's purse, goutweed, butterbur, cow parsnip (hogweed), coltsfoot, goosegrass, hawkweed, heather, hedge parsley, knotgrass, nipplewort, yarrow, salad burnet (small burnet), dock; crucifers: arugula (aka rocket), turnip greens, yu choy, rapini leaves (a.k.a. broccoli rabe/rape), kohlrabi greens, mizuna (Chinese greens), chard, cauliflower leaves
3 months old is a perfect time to introduce "salad" (fresh, dark, leafy greens) into your bunny's diet! Before 3 months of age, fresh greens can make bunnies sick. At this age, the salad should be small - less than 1/2 ounce, or 1/3 of a cup. (At 7 months you can start increasing the salad portion until, at 1 year, the rabbit is eating adult portions.)
Whenever you introduce a new food to your rabbit, be careful. Sudden changes to a rabbit's diet can cause illness. Stick to one new plant at a time, and wait a week or so before trying a new plant. Start small (a single bite), and increase portion size gradually. Watch for signs of illness (see related question below for details).
Be careful with cruciferous veggies. Many of the veggies listed above are crucifers (like bok choy, broccoli, kale, and others). Crucifers can cause gas in rabbits, and gas can be very serious, even leading to deadly illness (GI stasis). Bell peppers can also cause gas.
Be careful with lettuces. Too much can lead to diarrhoea.
Be careful with plants high in protein (like alfalfa, clover). They're great for rabbits younger than a year, but adult rabbits should only eat them as a treat because too much protein can lead to illness.
Wait until the bunny is 6 months old before introducing "treats." Any fruit and non-leafy vegetable (like carrots, pea pods, etc.) is considered a treat because it's relatively high in starch/sugar, and too much can make a rabbit sick. A healthy treat portion is no more than 2 tablespoons per day for a healthy, 6 pound rabbit. Commercial rabbit treats, and whole grains (like oat groats - this is NOT the same as oatmeal or processed grains), should also be kept away until about 6 months. (Many vets advise skipping these unhealthy foods entirely, though.)
Aside from salad, a 3-month old rabbit should have unlimited access to pellets, hay, and water. The hay can be alfalfa or a timothy-alfalfa mix. At 7 months, you can start transitioning the rabbit to an adult diet, which means only grass hay (like timothy - no alfalfa), and limited pellet portions (which depends on the weight of the rabbit).
See the related questions below for more details about a healthy rabbit diet.