A counseling specialist told me recently that in the past, children would naturally eat when they were hungry so when they would pass up food, you didn't have to worry because they would eventually get hungry enough to eat what you put in front of them. She said they have done recent studies, however, that show this does not seem to be the case anymore. They are not sure of the reason for the change, but children can nutritionally starve themselves now, particularly when it comes to foods they don't like, so it's important to "make" your kids eat a healthy balanced diet, without it being a struggle.
The reason I got into this conversation with this counselor is because my son is slightly underweight and a very picky eater. She recommended that I require him to eat at least one bite of whatever it is on his plate that he won't touch at each meal and that eventually, he will do it on his own. What is happening now in the process is he won't eat most of what I put on his plate, but he'll ask for a snack, like graham crackers or a glass of milk to fill him up. We tell him that he can't have those things because he didn't eat his dinner. Sometimes he'll eat some of the healthy stuff and then we'll give him a little of what he asked for. Sometimes he doesn't eat any of it and he doesn't get what he wants.
We do give him an Ensure nutritional drink every morning, which is something that he loves, so I'm pretty confident he is getting at least some nutrition every day. We also try to make sure there is something that I know he likes on his plate for every meal so I know he'll at least eat some of that one thing. With your son and the grapes, that's exactly how I would have handled it. If all he ate was three grapes, that would be just fine. He wouldn't get anything else until his healthy mid morning snack or he'd go back and finish what he had for breakfast.
My daughter is a big veggie eater and always has been. My son won't touch a veggie unless you make him so that's what we do. We don't make it a test of wills though. He just knows he won't get anything else until he takes at least one bite of everything that is on his plate. I can tell when he's hungry because he'll do it without having to be told twice. Other times, he just waits until his before bed snack and seems to have no problems. Just now he told me he wanted to give his lunch to his sister because he was full. I told him no, that he needed to eat his own lunch. I know he won't eat it all right now. But I'm willing to bet in about an hour, he'll get hungry and he'll go back and eat the rest. If not, he'll have something different to choose from at his afternoon snack time.
I think if your pediatrician is not too concerned by your son's current weight, and you're following his suggestions, he is probably fine. You might want to ask if you can add something like Pediasure or Ensure or a vitamin supplement. I know that makes me feel a lot better knowing my son is not getting all his nutrients in his food. I also think it's ok to make rules about kids having to at least take at least one bite of whatever is on their plate, without it being a power struggle. The main rule in my house, at least for my older kids, and it will eventually be the same for my youngest once he understands the concept, is you don't have to eat anything else on your plate but your vegetables, but you have to eat all your vegetables if you want anything else. I don't care if they leave everything else on their plate, as long as they finish their vegetables. They have never actually not eaten at least a portion of the entree and the other side(s) 'cause I tend to make things my family likes, but it's an option if they want. That is a way to share the power and control so they don't feel like they are being forced to eat everything, but at the same time, I'm making sure they get the most nutrition they can at each meal.
Blessings,
N.