Okay, although my son would eat some veggies (broccli steamed and raw tomatoes)- he wouldn't eat meat for a while, and has been awful about tasting new (to him) things.
Some things we did that helped:
We would let him have an alternative meal for a while, if he tasted willingly at least a bite of other things offered. So, don't make the PB sandwitch or the bowl of mac and cheese until they've tried a bite of the real dinner.
Mix in veggies with the mac and cheese. Peas, diced tomatoes, spinach and broccli pieces go nicely with kraft dinner.
make fruit smoothies with yogurt, a bananna (you can freese peeled banannas for smoothies), milk and fresh or frozen bagged fruit (the frozen fruit lasts a while longer then the fresh). They think they're having a milkshake, not fruit. And they're getting used to fruit tastes without much added sweetness.
Have a "picnic" tasting party dinner - serve baby carrots, bell pepper strips (yellow, red and orange are sweeter than green, and are preferred in my house), grape tomatoes, and a little veggie dip of some sort. spread out a sheet or tablecloth on the floor, and enjoy a picnic inside. the change of routine may make them more likely to taste the veggies.
My son, when he wouldn't touch meat, liked tofu nuggets. take firm tofu, cut it into bars, soak it in broth (beef, veggie or chicken) overnight, coat the marinated tofu in shake n bake (or breadcrumbs) and bake (I think at arounf 300 for 10-20 minutes). He loved them until he got used to the texture of meat.
Talk about nutrition with your kids, how different foods have things your bodies need to help them grow and stay healthy. Involve them in shopping, especially in the produce isle. Consider having them help you choose a "mystery fruit/veggie" (one the kids are not familiar with) every shopping trip for the whole family to try.