If he’s over 9 weeks, I would introduce one green leafy staple, like romaine (which has a strong flavor) or green leaf lettuce, which is mild. only use that for at least 2 weeks or longer. Just about a 1/2 cup maximum should be fine. Definitely read through the Diet section of the site, and also go to the Diet section of HRS, http://www.rabbit.org. (House rabbit society)
What you want is to very slowly introduce veggies, with little change and variety at first. So, don’t try anything new without spacing them apart by 1-2 weeks at least. A bunny will not get bored when they are young. But their tummies are delicate so any change can temporarily disturb their digestion. A tiny carrot treat is fine.
NBO123: If Sally is now 6 months, I would do the opposite and start trying her on new veggies. Not quickly, but if she isn’t eating what you’ve tried, it may be a family of greens she doesn’t like. Like broccoli, kale and romaine are all in the strong tasting family, the green leaf, parsleys and mint are much softer flavors for example. Try what isn’t like any you’ve tried before and see if she just has a preference. Sammy loves romaine and hates red leaf, for example. You want to find about 3 staples that she will eat routinely. Cut back on pellets or treats (but continue unlimited hay) in case she’s filling up on those and doesn’t have room for the “good dinner” foods.