OP, your child is overall small. Low percentage of weight AND height isn't worrisome. Falling off a chart, large drop in percentage, basically changed in percentages can sometimes be indicative of something. My 7 year old DS has always been 5-10% for weight but just fell off the chart last year. Our ped was unconcerned since he has always been low on the chart. Plus he will eat two 5 Guys burgers. We think he has a hallow leg.

Just feed him what he will eat and don't focus on meat as long as he is getting good protein from other sources.

OP, I also have a very small child -- under the percentile chart -- and we are concentrating on getting as much nutrition and calories in as possible but we still don't count calories. We simply obtain the most calorie-packed foods possible in the categories she will eat, add calorie-dense options if possible (avocado, butter, mayonaise, syrup), and urge her to fill up. Running daily calorie statistics with an underweight child is unhelpful and really disheartening because one day they may eat quite a bit and the next day very little. And that's normal.

My 7yo always finishes her happy meal hamburger

I'm a vegetarian and do most of the cooking. Dh grills once a week or so. My 2 yo eats almost a whole burger with bun and some veggies. It's good protein and red meat doesn't usually happen more than once a week. He doesn't fill up on processed food and snacks. He is still 50th percentile and a good eater and very active. I cannot begin to guess how many calories are in any of his meals but he eats fruit everyday, veggies almost every day, meat and chicken a couple of times a week, eggs, dairy, quinoa and other grains, yogurt....and special treats often enough where he isn't deprived, but not daily. He stops when he is full. He eats when he is hungry. I never once have thought about the calories in any of it. Focus on quality and not quantity.

It is strange you refer to it as meat exposure and count calories. You sound more like his nutritionist than his mom. So clinical and controlled. It really sounds too like you think vegetarian is better and you are trying to find reasons to tell dad no more 'meat exposure', and you have a my food and your food divide.

I have never followed any calorie count even with my picky eater. We did our best to get healthy rich foods into him but we never counted calories.

If he had celiac and was eating gluten he may not have been absorbing nutrients well. He will likely gain weight as he gets healthier.

Op here, to clarify, DS is skinny, 40 lbs at 6 yrs, smallest in his peer group, 5th percentile for weight, 25th percentile for height. Recently diagnosed with celiac, which had caused lot of gagging, reflux and food aversions in the past, just getting over it. Now eating out is limited to once a week as tough to find gluten free foods he likes, before it was school lunches and 2 to 3 times per week of meat exposure, now only once on the weekend. So DH grills once a week as well, but agreed DS likes my vegetarian food better, he is more used to it. Yes sure he leaves his foods sometimes, not always.
He says he likes burger, eats half, then says he is full, but has room for my food if we give him the choice. Happened past few weeks. he has food jags, loved hot dogs straight for a year, then stopped it completely. So was wondering if he is slowly phasing out of burgers as well, anyways I will know soon from him.

We are making sure he gets enough to grow stronger and taller, but is also exposed to different kinds of foods and can hold on to what he has eaten. Obviously he will eat less of his less favorite food and more of his most favorite foods, so I have to balance between variety and growth.

Thanks for all the helpful comments, I guess I will do bits and pieces of fruits and veggies with burger like the other days, as well as keep a backup food or let him compensate at other meals.

I know some of you are averse to calorie discussions, but curious, how many calories would a 40 lb, 6 yr old need. Maybe I should call ped, but sites/books vary between 800 to 1400, what is a general guideline to follow to make sure he does not go off the charts?

You seem to have a very unhealthy relationship with food OP and you are putting this on your child. If half a burger fills him up then fine. On a day he is hungrier he might eat a full burger.

You are a control freak. You need to stop micromanaging, deal with your anxiety, and let your husband grill his burgers and your son eat what he can.

Very odd that you're counting calories and trying to decide if he likes burgers.

My 2.5 year only usually finishes a whole burger plus some sides. My 5 year old will have half a burger and 7 chips and pronounce herself full.

Where are your sides???? Corn? Salad? Guac and chips? Grilled veggies?

My 6 year old will finish one off every now & then, but usually just eats 1/2 - 3/4.

A mini-burger and some sides sound like good ideas. I'd follow your DS's lead on how much he wants to eat.

My 13 year old ate a whole burger at line 3 or 4 my 11 year old just ate one for the first time this week. Both are thin or healthy weights. Let your kid decide when he is full and stop eating. Also why not add some veggies or fruit to the meal?

My absolute #1 concern is not whether the child finishes the meal, but why you are counting calories!?

What is your household rule regarding finishing a meal and portion size throughout the week? Must he always clean his plate or is that a rule simply for meat night?

Help your child learn what it is to feel full and let him stop eating at that point.

Can you adjust the size of the burgers? McDonald's hamburger and double quarter pounder with cheese are both burgers but the amount of food involved is vastly different, for example.

A burger, bun, and cheese with no vegetables (lettuce, tomato?) is bot a very balanced meal.
If your son is used to eating vegetarian the rest of the week, requiring him to eat an entire burger is a pretty heavy meal.
Why not compromise and make him a mini-burger with sides? Also, he seems old enough to voice his own opinion as to whether he likes the taste/texture of beef.

Flowchart. Is kid full? Stop eating. Is kid hungry? Keep eating.

OMG. Stop. You sound crazy.

Why not eat vegetarian at home and eat meat when eating out?

Plus stop counting the calories!

We eat vegetarian at home, but DH grills meat once a week, and he expects our DS to eat the whole hamburger, which is roughly 400 calories with burger, the bun and 1 slice of cheese. Do kids typically eat the full burger? 6 yr old 40 lb DS only eats half. This is the only dinner item today, no sides. Trying to figure out if it is the taste/type he dislikes or half a burger is good enough? I agree 200 is less , he needs 300, but kids can adjust calories across meals. We are wondering whether to continue the grill.