You don't even have to make them eat veggies all the time. Toddlers especially are picky eaters in general and they might like only one kind of veggie then the next week are put off my another type of food the following week. Sometimes they are put off by all greens. This is pretty normal. The important thing is to teach them not to eat/snack all the time, eat at mealtimes, let them have their stomach growl and wait for dinner for example.  It's not just teaching them about nutrition and that certain foods can make you fat but that food is something you reach for when you are actually hungry and that you can wait for things like mealtimes. And /u/SkinnyMcShitlord is right, sometimes if you keep giving them certain foods, they take to it all of a sudden. But with this kid, to be this fat, is straight up child abuse. Children at this age don't have set psychlogically related eating habits like us adults (like eating out of stress or worry).  They were probably stuffing this child forcefully the whole time. Little kids can regulate how much they want to eat. Sometimes they skip meals, sometimes they are like a bottomless pit, especially when they are having a growth spurt. They must have been forcing him to eat even when he said he was too full.