My two youngest sons are the most enthusiastic of the three about helping in the kitchen.  The other night while I was preparing dinner, my youngest came in and shouted, “I want to help!”.  Now often if I try to help him help me, he often shouts, “I can do it!” (He’s a loud boy and really wants the independence of accomplishing it on his own.)  Well, since I’d done most of the prepping/cooking already, but my husband just got home and said he’d help by shucking the corn (local white corn, so delicious!), my son joined him out on the back deck to shuck.  It was the cutest sight, especially since the wee man was in his hot-weather-comfortable (lack of) clothes. 
My husband showed him how to remove the silk from the corn by rubbing a tea towel along the ears. 

The next night my husband made crab cakes and salad for dinner.  The chorus of “I want to help!” resounded before he’d finished processing the bread for bread crumbs. So this time they helped in making the crab cakes (“Form balls then smush flat.”),
peel carrots (“Turn them around so you’re not peeling it away to nothing.”)
and grating the carrots and beets (“Careful when it gets small so you don’t cut your fingers.”).
  They loved their dinners both nights and my youngest said “It tastes even better when I help make it!”  One of my girlfriends said that’s because you put love in as an ingredient.

Getting them to help in the preparing of the meals, especially the vegetables, might be the trick if you have reluctant eaters.