We belong to a CSA, so I know a lot about cooking and eating veggies that you (and your kids) dont like. Ill go from worst to best.
Brussel Sprouts - You either like em, or you dont. I love them roasted or steamed with a little S&P (and maybe vinegar), but no matter how you cook them, they still taste like brussel sprouts.
Kale - Baked chips is the only answer. Its easy and its not bad tasting (note, I didnt say good). Kale is very bitter and the leaves are substantial (you cant really hide it). There's really no other good way to eat this without making is unhealthy (ie: adding butter/greasy meats/cheeses/etc).
Broccoli - Lightly steamed (dont overcook!). Salt, pepper, maybe a little lemon juice is good for me. My kids dip in a little ranch. If they can eat it and not complain, it should be palatable to anyone. Make a lot and the key is to eat it first while its still hot and you're still hungry. If you wait till its cold and the last thing on your plate and it will taste like ###.
Cauliflower - Roasted. This one takes time, but is worth it. I double the recipe and eat it all week. Cut 1 head of cauliflower and 1 medium onion into uniform pieces. Add 6-8 small whole cloves of garlic and 4 sprigs of Thyme. Toss is all in 3 Tablespoons of olive oil. Roast it in the oven at 425 for 40 minutes (I just lay a sheet of foil on the rack - easy cleanup). Remove veggies, toss with 1/3 Cup of Parmesan and roast for another 15 minutes. I usually add sun dried tomatoes and toss it with some 100% whole wheat pasta. Excellent, healthy meal.
Here's how I like a couple other of the super-foods...
Beets - I like to peel and slice them raw, stuff them in a mason jar and quick-pickle them. Boil 1C water + 1C vinegar + 2TBSP salt + 1TBSP Tabasco. Pour into jar and seal. Ready in 24 hours. Keep in fridge as snack.
Sweet Potatoes - Peel and slice into rounds. Toss in olive oil and bake at 400 for 40 minutes. Again, I just use foil on the rack. They will get brown and almost sticky on the outside. Oven temps will vary, so keep an eye on it. May take longer. These are great with any meal.