I'm in the same boat. Adrian is tall and skinny. Actually, I have a doctor's appointment today to check on his weight because he didn't gain any since 9 months. Yes, he is very active and has been running for quite a while now. Generally eats well, but not a meat eater. Here are some things that I do.
As people said, no chaising around with the food (although I admit, I do that when he is sick and won't take anything :oops: ). At these times, baby oatmeal with apple sauce is about the only thing he'll eat.
If he wants to eat, give him food.
Set up his healthy snack food supply somewhere where he can get to it, like lower shelf in the pantry. I noticed Adrian discovers the snacks, takes what he wants and brings it to the high chair.
Find things that he likes to eat. He tends to like things with more taste, but I'll give him whatever he points to during dinner (if he points to something, he usually eats it). He really surprised me couple of days ago, pointing to a lamb roast. I cut little pieces and gave it him, and he ate it! That was the most meat he ate in a month. Loves the cheese, I always have some for him. Surpirsed me last night, eating some buffalo meat in a gravy. Maybe he liked the gravy and the meat wasn't dry?
Offer smaller portions and meals in courses. I found that he is more likely to eat, if there is less food on the plate and fewer choices. Two foods on a plate seems to be the most he can handle. I start with the food I would like him most to have. Once done with particual course, either give a refill or move to a new food.
A hit that he likes for lunch is enriched grilled cheese sandwhich.
Between two pieces of bread (whole wheat) put cheese, some lean lunch meat, and tomato slices and grill in George Forman grill or alike for couple of minutes. Serve with fruit smoothie.
Be sneaky.
Add some chopped meat to the vegetable, add some garlic, herbs.