Second the roasted vegetables. The secret is to blast them on high heat, after cutting them in medium-small pieces, tossing them with lots of olive oil (more than you'd think, the veggies all need to be well-coated but not dripping) and some salt. Spread them out on baking sheets so that they roast and don't steam. I usually set the oven for 425, although I watch carefully and toss the vegetables and rotate the pans at least once.
Works for:
cauliflower
cabbage (cut in half, remove core, and slice thinly from pole to pole)
Brussels sprouts (shred them or cut in quarters)
broccoli
green beans
carrots (advanced users can add some whole cumin seeds)
butternut squash
and others
http://www.thekitchn.com/how-to-roast-any-vegetable-101221
We usually roast one type of veggie per tray -- mixing them gets challenging because of different cooking times.
Roasting takes away a lot of the bitterness and caramelizes the natural sugars.
Baked sweet potatoes are also really good. I am perfectly fine if my kids slather theirs in butter or olive oil.
I think cooking makes many vegetables a lot more palatable, not to mention easier to eat in quantity. I love roasted cauliflower, but I can't face eating more than one floret of raw.
Our kids have developed a taste for more varieties of veggies as they've gotten older, but steamed broccoli and steamed baby carrots have been on the menu pretty much every night for years even though we add in other veggies now too. I figured if they're getting one green and one orange at dinner, we're doing fine.