First, you really cannot MAKE a child eat something they don't want to eat. It's important NOT to create food fights. Plus you probably don't want to fight with your young children! So best is to take advantage of their natural instincts to put things into their mouths and to explore. Food is one example. To help the young child 'learn' to like foods, simply keep placing the food on his/her plate, along with other foods they enjoy eating, and then leave him/her to explore the plate. Set an example by eating your plate of same foods. But don't force the issue. It can take 15 attempts at this before they begin eating the food. And sometimes they may still refuse it- in which case it's best to move on to some other food! It is always reassuring to know that kids do somehow ingest the nutrients they need to remain healthy.
More information is available in a book for which I was coauthor: "Feeding Your Child for Lifelong Health" (Susan Roberts and Melvin Heyman) -- an exerpt is found at the link attached.