If they don't make an honest attempt, the plate gets wrapped in plastic, stuffed in the 'fridge, and microwaved for the next meal; repeat until they do or it's 3 days old. Although it usually isn't necessary, you can escalate things by making the second meal that everyone else gets to eat something they really like.
Not every kid wants to be part of the meal making and planning process, but that also works well. A bit of the carrot and stick approach, basically.
Ground meats are your friend; you can stuff vegetables in them reasonably easy if necessary; even hamburgers prepared with diced veggies w/sweet potato fries isn't a terrible meal nutrition-wise.
Not every kid likes pickles, but if they do, virtually every vegetable can be pickled and they will eat it. Commercially prepared pickles tend to be very high in sodium and sugars but maybe you know someone (if they are into home canning, they almost always make more than they can eat themselves) or there is a Farmer's Market that doesn't assume you're a millionaire you can buy from.
You are up against what is a huge availability of alternate non-home food options, so that limits the effectiveness of some old-school solutions. But as long as they like *something* you can use that to encourage them to eat what is on their plate.
Kids will eat most things if you put it between slices of bread.
Kids will eat most things if you make it into a soup or stew.
Stop feeding them juice. Give them an orange to eat, versus a glass of orange juice, which has the (natural) sugars of a half dozen to a dozen oranges and no roughage, is generally made from green oranges and is blended in vats which may have some juice that is up to 12 months old before bottling.
Apple Juice (the cheapest form of fruit juice) is tooth decay in a bottle. AVOID. Beware fruit juices which are just flavoured Apple Juice.
