Easy does it
Children's palettes take a while to develop.
Putting too much pressure on them to eat a variety of foods when they don't want to could wind up having the opposite of your intended effect. The best way to teach is by example so set a great one. Offer lots of choices. And make food fun, because if it's fine you're likely to enroll them. If it's a burden, you're likely to push them in the wrong dir.