SPD or other special needs), but here's what has worked for us:
Cut Out Refined Carbs
This is the biggest thing for us - if my children know that there are crackers, goldfish, cookies, chips, pretzels, or other refined sugars/starches they will refuse nutrient dense foods and hold out for the refined stuff. I think this is most likely the cycle most parents get stuck in- their children self limit (mine will too) to these foods and they're afraid that if they don't give them to them, they won't eat anything at all. For us, we had a few weeks with *none* of this in the house so they could get used to good nutritious food. Yes, this is a big step, but I attribute all the variety of foods my children happily eat to breaking them of the nutritionally-void food habit. After a few weeks of *none* we do have chips, pretzels, and even ice cream in the house again. It's mostly for Dad, and sometimes for Mom when the kids are in bed.
I like the idea of moderation for things like this with little ones, but it just doesn't seem to work for us. If they know they can have it 'sometimes' and it's in the house, they'll hold out for it. It's not too bad for hubby and I to wait til they're asleep before we break out the ice cream- it also keeps us eating nutritious foods all day long too :)
Eating in Front of the Kids
Our kids love to eat what we're eating. And hubby and I enjoy all the foods listed above (other than the cod liver oil!) so the kids know that's our every day food. They're young and eager to try out all of what mom and dad do (including doing the dishes... 'helping' with laundry... 'organizing' the pantry). Sometimes even if they have the same thing that I do on their plate, it's more appealing if it comes from my plate. In that case, it doesn't bother me to feed them off of my plate, or sometimes I'll just get them started and then show that they really do have the same thing on their plate. More often than not they're happy to finish their meal on their own.
Taking the Pressure Off
My children were both slow to start eating- they enjoyed playing with food, but didn't actually swallow much until a few months past their first birthdays (they were breastfed- my 16 month old still is). I've never really put too much worry into how much they eat. My daughter goes in spurts, I'd guess this is normal. For a week or so every once in a while she'll only eat a bite or two of her protein (eggs, meat) for a meal and half of her fruit/veggies. I just note that she's eating less right now and make a note to serve her less at her next meal. She knows how to ask for more when she's hungry again. She'll also compensate the opposite direction and eat more than I do for a week at a time, I think it all evens out and I don't try to change her.
That's what's seemed to work in this house so far. How about you? How have you had good results getting your children to eat a variety of food?