I was the child who had parents who thought I should eat "enough". I don't think we particularly had no pudding if we didn't eat enough, but my parents had a thing about me eating enough carbohydrates. This meant either mashed potato or brown bread. I now eat neither, and even the smell can make me vomit.
I still have a poor relationship with food.
Now the thing was I had a reputation in our family as being a picky eater. Looking back I wasn't. I didn't/don't have a huge appetite. Genuinely I had eaten enough. But actually the situation was that I didn't like the same food as my parents-which was very traditional British food. Toad in the hole was about as adventurous as it came (and yes, we did get mashed potato served with that).
My siblings liked that. I didn't.
We once went to a posh restaurant for my grandparents' ruby wedding. I remember sitting there awed by all the lovely food. They brought a trolley loaded with what I though of as really exotic food (like salmon!!) and served you what you wanted. I think I tried everything!
My brother took one look and said "I'd rather have bangers and mash" and my sister stuck to the one dish she knew.
As an adult, I realise that actually I was far more adventurous with food than they were. I was very happy to try different foods and often like it. But they liked the staple diet we had, which I didn't.
Have a think about it. Are you asking them to eat food they really don't like? What purpose is it to make them eat that? I'll tell you it's pretty miserable looking at a plate of food and not wanting to eat it.
Dh's family had a policy that they had to have a bit of everything and eat it all-even on Christmas day. There's only one thing dh really hates and that's sprouts. Actually I suspect if he ate one, he'd quite like it. But his memory of sprouts as a child was being forced to have one-why? He'd have happily eaten more of other vegetables, and it never would have been the only vegetable. The result is that he won't try them now.
Make a list of what they like. Is it reasonable? Are they consistent? Can you make sure that there is always something decent that they like? I prefer raw carrots, so often eat mine raw. Is that a problem? No. Does it matter if one meal all they eat is raw carrots? No. Just make sure the other meal has other food types-do cheese on toast or pizza with extra cheese or something.
Get them to help cook when you're doing something new. Children often will try things they've made that they won't otherwise. Praise them for trying things, and don't make them finish it if they don't like it.
And don't give them a huge portion. I used to find a huge portion made my appetite disappear immediately. I knew I wouldn't finish it, so it felt too much to begin.
For my dc, I have one who as a baby ate everything, then was ill as a 8yo and then ate a very limited diet after that.
One who ate nothing as a baby (only thing she'd eat consistently was tinned sweetcorn) and now eats fairly well, but always had a small appetite.
One who always will try things and eats well all the time.
So for the first one, I would make sure that every other meal was something she'd eat. But if it was something I knew she really didn't like, then I'd do her a baked potato and cheese, or I'd have a pie that she could eat 1/4 at a time. It was a boring diet, but she survived. The one thing I didn't allow was liking something the day before then refusing it the next. She's now an adult and eats a healthy diet, not hugely varied, but that isn't a problem.
With dd2 if she hadn't eaten much for a couple of days I'd do a tin of sweetcorn. Gradually she learnt to try things and eat more, never put pressure on her to eat, and now she eats most things (except melted cheese).
Ds I know he's really ill if he doesn't eat, so never a problem!