The other way to get fat is when your mom or dad use the phrase "Finnish all the food on your plate!" Just think of the ethiopian children who have no food on their plate!
That type of parenting will get your kids fatter quicker than anything else.
Depends on what the food is on your plate. If it's all crap that's high fat, high cholesterol, high carb...then yes.
If it's something that's actually good for you, like lots of fresh vegetables, then absolutely...finish it.