This topic has a wide variety of answers on the web but it's one of the most asked questions for new bunny owners. Is it safe to feed your baby bunny fresh produce?
You can feed your baby bunny fresh veggies from the day they come home at 8 weeks old but only a limited amount starting out with. I suggest starting veggies and fruits as more of a treat to slowly introduce them. I always tell my families no more then the tip of your pinky for fruits or veggies that are high in sugar. Any change in a rabbits diet needs to happen slowly especially when introducing new vegetables. After your bunny is 3 months old you can increase the amount of veggies given daily to about a small handful or a quarter of a cup (doesn't have to be an exact measurement, this is just an estimated guide to follow). Each month after that you can increase the amount of veggies you are feeding them until you reach 6 months old. After 6 months, depending on your rabbits weight, you can start feeding them more. A good guide is 1 cup per 4lbs. of rabbit per day.
Fruits should only be given as a small treat as they are high in sugar! I If at any time you notice that your rabbit is starting to get soft poo, which will look different then cecotropes, then cut out fruit completely from their diet and mainly just push hay with small amounts of pellets. Rabbits diets need to be high in fiber which is why hay is so important and should be 90% of their diet. After a few days their poo should harden again to small little round balls.
There are a lot of online sources and breeders that are extremely against feeding rabbits under 6 months old any kind of fruits or veggies and to each their own. I've been raising rabbits since 2011 and have owned rabbits since 1997 and have never had an issue feeding the way I have described above. There are several families that don't like to feed their rabbits commercial pellets either and will transition their baby bunnies to fresh veggies and alfalfa hay within the first month of taking them home and that is safe to do. Each rabbit will respond differently to transitioning as well so always take it very slow and be watchful of their poos to make sure they stay hard and round! Also it's smart to consult your veterinarian for feeding advice as well!