It took me ages to work out what evm meant. Asked DH and he knew in an instant. My obese DH. Just saying. Having an acronym on hand for a McDonald's order suggests it's a frequent treat.
I participated in research for a university on healthy eating for kids. I did this because I've always been concerned about giving DS A healthy balance diet. They shared the results with me and analysis of my answers.
I'm overly cautious towards healthy eating and have a tendency to overestimate how many calories and how much salt and sugar are in a portion. This was based on 100 questions about my attitudes towards parenting, healthy eating and my own childhood. I then reviewed 20 meals and estimated calories sugar and salt.
The wider results were that those who had concerns about healthy eating would overestimate portion size and calorie content etc. They linked poor diet knowledge to lower education attainment levels, Study was across 20,000 or so. Those who underestimated how much was in different meals had less overall knowledge about what makes up a healthy portion or meal.
I found the results interesting and they helped me to relax a little and not feel the need to count the number of salt grams per day iyswim.
So when it comes to blame, I don't think that's useful. But primary carer is ultimately the person buying the food, cooking the food and sanctioning treats.
I know my relationship with food isn't great which is why I have put a lot of effort into ensuring my son does not suffer from the same issues. Maybe this is an area you should look at?