A slightly more scientific perspective.
A study done called 'You Will Eat All of That! (A retrospective analysis of forced consumption episodes)' found that pressuring children into finishing their food may lower their natural appetite (perhaps because they're being told when and how much to eat, rather than learning naturally).
Other studies have also found that it may lead to over-eating in adulthood (as you may be encouraging them to eat after they've stopped being hungry), and that it may actually inhibit their growth.
You might also find it helpful to know that another study named ''Finish your soup’: Counterproductive effects of pressuring children to eat on intake and affect' found that in children who were pressured into eating certain foods (e.g. vegetables), those children were more likely to gain an aversion to those foods that lasted into adulthood.
This blog post has an overview on the topic, but he's an excerpt from the end: (emphasis added by me)
As a parent, you naturally feel anxious if your child is doing
something that you think is unhealthy, like not eating "enough."
Reassure yourself that in all but the rarest of cases, children will
eat enough food to survive and be healthy.
Notice the times when you feel tempted to pressure your child to eat.
Relax, take a deep breath, smile, and say to yourself "Oh well. His
brain knows how much he needs to eat." Then go do something else to
distract yourself.
The following behaviors are perfectly normal! Don't get scared into
pressuring your child to eat when he does them.
- refusing to eat a meal
- eating a lot of food for a few weeks, then eating practically nothing for the next few weeks
- refusing to eat certain foods
- eating less than a sibling, neighbor kid, or cousin
- being so excited by toys and people that he doesn't finish his meal
To get your child to eat at mealtimes, try these techniques:
- Sit down and eat the same food as your child.
- Children often need to try a food many times before they like it. Feed your child healthy foods for each meal, and be patient in the knowledge that they will probably eventually like them.
- If your child is easily distracted, you can gently call his attention back to his food. Do this only occasionally, so that he does not feel pestered, and only do it when he's first starting his meal, so that he does not eat when he is no longer hungry.
- Don't worry.
You might also want to consider why you are pressuring your child to finish. Did her supper take a lot of work, and perhaps you don't want to see it wasted? Perhaps you should prepare lighter suppers in the future. Are you worried that they will snack later? Why not buy some healthy snacks, like apples, breakfast bars, or healthy crisps. Or, if you're worried about a snacking habit developing, perhaps you need to move around your dinner times a bit to suit your child's appetite?
Try to consider these things from your child's perspective, and remember they aren't intentionally trying to waste food or annoy you. Best of luck!